Compressive encoding apparatus, compressive encoding method, decoding apparatus, decoding method, and program

ABSTRACT

The present disclosure relates to a compressive encoding apparatus, a compressive encoding method, a decoding apparatus, a decoding method, and a program which can provide a lossless compression technology having a higher compression rate. An encoding unit of the compressive encoding apparatus converts M bits of a ΔΣ-modulated digital signal into N bits (M&gt;N) with reference to a first conversion table, and when the M bits are not able to be converted into the N bits with the first conversion table, converts the M bits into the N bits with reference to a second conversion table. When the number of bit patterns of the N bits is P, the first conversion table is a table storing (P−1) number of codes having higher generation frequencies for past bit patterns, and the second conversion table is a table storing (P−1) number of codes having higher generation frequencies for past bit patterns, which follow those of the first conversion table. The present disclosure is applicable to a compressive encoding apparatus that compressively encoding an audio signal, and the like, for example.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No.PCT/JP2016/054723, filed in the Japanese Patent Office as a Receivingoffice on Feb. 18, 2016, which claims priority to Japanese PatentApplication Number 2015-040886, filed in the Japanese Patent Office onMar. 3, 2015, each of which is hereby incorporated by reference in itsentirety.

TECHNICAL FIELD

The present disclosure relates to a compressive encoding apparatus, acompressive encoding method, a decoding apparatus, a decoding method,and a program, and particularly, to a compressive encoding apparatus, acompressive encoding method, a decoding apparatus, a decoding method,and a program which can provide a lossless compression technology havinga higher compression rate.

BACKGROUND ART

Recently, music distribution using high-resolution music which is audiodata having higher sound quality than a music CD (CD-DA) has beenperformed. For pulse code modulation (PCM) music such as 96 kHz/24 bits,there is a lossless compression technology (reversible compressiontechnology) such as free lossless audio codec (FLAC) that is used fordistribution.

Further, for ΔΣ-modulated digital signals (direct stream digital (DSD)data) which are not PCM signals but are 1-bit signals, there is atechnology called direct stream transfer (DST) developed by Philips as alossless compression technology and this technology is used tomanufacture a super audio CD (SACD).

However, this technology is based on 1-bit signal processing and is notsuitable for software processing in a CPU based on processing in bytes,and thus is mounted as hardware (LSI) in an SACD player and the like.Since high throughput is required for processing through software,processing cannot be performed in a general embedded CPU.

Accordingly, there is a demand for a lossless compression technologywhich enables processing even in a general embedded CPU whileconsidering execution by mobile terminals when audio signals aredistributed using DSD data.

The applicant has proposed a technology for compressing current datainto 2 bits with reference to past data in units of 4 bits in PatentLiterature 1 as a lossless audio signal compression technology using DSDdata.

CITATION LIST Patent Literature

Patent Literature 1: JP H9-74358A

DISCLOSURE OF INVENTION Technical Problem

However, a data compression rate is not so high in the technology ofPatent Literature 1, and thus a lossless compression technology having ahigher compression rate is required.

The present disclosure is devised in view of this situation and enablesprovision of a lossless compression technology having a highercompression rate.

Solution to Problem

According to a first aspect of the present disclosure, a compressiveencoding apparatus includes an encoding unit that converts M bits of aΔΣ-modulated digital signal into N bits (M>N) with reference to a firstconversion table, and when the M bits are not able to be converted intothe N bits with the first conversion table, converts the M bits into theN bits with reference to a second conversion table. When the number ofbit patterns of the N bits is P, the first conversion table is a tablestoring (P−1) number of codes having higher generation frequencies forpast bit patterns, and the second conversion table is a table storing(P−1) number of codes having higher generation frequencies for past bitpatterns, which follow those of the first conversion table.

According to the first aspect of the present disclosure, a compressiveencoding method includes converting M bits of a ΔΣ-modulated digitalsignal into N bits (M>N) with reference to a first conversion table, andwhen the M bits are not able to be converted into the N bits with thefirst conversion table, converting the M bits into the N bits withreference to a second conversion table. When the number of bit patternsof the N bits is P, the first conversion table is a table storing (P−1)number of codes having higher generation frequencies for past bitpatterns, and the second conversion table is a table storing (P−1)number of codes having higher generation frequencies for past bitpatterns, which follow those of the first conversion table.

According to the first aspect of the present disclosure, a program thatcauses a computer to execute a process of converting M bits of aΔΣ-modulated digital signal into N bits (M>N) with reference to a firstconversion table, and when the M bits are not able to be converted intothe N bits with the first conversion table, converting the M bits intothe N bits with reference to a second conversion table. When the numberof bit patterns of the N bits is P, the first conversion table is atable storing (P−1) number of codes having higher generation frequenciesfor past bit patterns, and the second conversion table is a tablestoring (P−1) number of codes having higher generation frequencies forpast bit patterns, which follow those of the first conversion table.

According to the first aspect of the present disclosure, M bits of aΔΣ-modulated digital signal are converted into N bits (M>N) withreference to a first conversion table, and when the M bits are not ableto be converted into the N bits with the first conversion table, the Mbits are converted into the N bits with reference to a second conversiontable. Here, when the number of bit patterns of the N bits is P, thefirst conversion table is a table storing (P−1) number of codes havinghigher generation frequencies for past bit patterns, and the secondconversion table is a table storing (P−1) number of codes having highergeneration frequencies for past bit patterns, which follow those of thefirst conversion table.

According to a second aspect of the present disclosure, a decodingapparatus includes a decoding unit that converts N bits of encoded datathat is obtained by compressively encoding M bits (M>N) of aΔΣ-modulated digital signal into the N bits, into the M bits withreference to a first conversion table, and when the N bits are not ableto be converted into the M bits with the first conversion table, decodesthe N bits into the M bits with reference to a second conversion table.When the number of bit patterns of the N bits is P, the first conversiontable is a table storing (P−1) number of codes having higher generationfrequencies for past bit patterns, and the second conversion table is atable storing (P−1) number of codes having higher generation frequenciesfor past bit patterns, which follow those of the first conversion table.

According to the second aspect of the present disclosure, a decodingmethod includes converting N bits of encoded data that is obtained bycompressively encoding M bits (M>N) of a ΔΣ-modulated digital signalinto the N bits, into the M bits with reference to a first conversiontable, and when the N bits are not able to be converted into the M bitswith the first conversion table, decoding the N bits into the M bitswith reference to a second conversion table. When the number of bitpatterns of the N bits is P, the first conversion table is a tablestoring (P−1) number of codes having higher generation frequencies forpast bit patterns, and the second conversion table is a table storing(P−1) number of codes having higher generation frequencies for past bitpatterns, which follow those of the first conversion table.

According to the second aspect of the present disclosure, a program thatcauses a computer to execute a process of converting N bits of encodeddata that is obtained by compressively encoding M bits (M>N) of aΔΣ-modulated digital signal into the N bits, into the M bits withreference to a first conversion table, and when the N bits are not ableto be converted into the M bits with the first conversion table,decoding the N bits into the M bits with reference to a secondconversion table. When the number of bit patterns of the N bits is P,the first conversion table is a table storing (P−1) number of codeshaving higher generation frequencies for past bit patterns, and thesecond conversion table is a table storing (P−1) number of codes havinghigher generation frequencies for past bit patterns, which follow thoseof the first conversion table.

According to the second aspect of the present disclosure, N bits ofencoded data that is obtained by compressively encoding M bits (M>N) ofa ΔΣ-modulated digital signal into the N bits, are converted into the Mbits with reference to a first conversion table, and when the N bits arenot able to be converted into the M bits with the first conversiontable, the N bits are decoded into the M bits with reference to a secondconversion table. Here, when the number of bit patterns of the N bits isP, the first conversion table is a table storing (P−1) number of codeshaving higher generation frequencies for past bit patterns, and thesecond conversion table is a table storing (P−1) number of codes havinghigher generation frequencies for past bit patterns, which follow thoseof the first conversion table.

Further, the program can be provided by being transmitted through atransmission medium or being recorded in a recording medium.

The compressive encoding apparatus and the decoding apparatus may beindependent apparatuses or may be internal blocks which constitute asingle apparatus.

Advantageous Effects of Invention

According to first and second aspects of the present disclosure, it ispossible provide a lossless compression technology having a highercompression rate.

Note that the effects described here are not necessarily limited, andany effect that is desired to be described in the present disclosure maybe exhibited.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example of a configuration ofa first embodiment of a compressive encoding apparatus.

FIG. 2 is an explanatory diagram of a method of creating a datageneration count table pretable.

FIG. 3 is an explanatory diagram of a conversion table table1.

FIG. 4 is a block diagram illustrating an example of a configuration ofan encoding unit.

FIG. 5 is a flowchart illustrating a compressive encoding process.

FIG. 6 is a block diagram illustrating an example of a configuration ofa first embodiment of a decoding apparatus.

FIG. 7 is a flowchart illustrating a decoding process.

FIG. 8 is a block diagram illustrating an example of a configuration ofa second embodiment of a compressive encoding apparatus.

FIG. 9 is a block diagram illustrating an example of a configuration ofa second embodiment of a decoding apparatus.

FIG. 10 is a block diagram illustrating an example of a configuration ofa third embodiment of a compressive encoding apparatus.

FIG. 11 is a block diagram illustrating an example of a configuration ofa third embodiment of a decoding apparatus.

FIG. 12 is a block diagram illustrating an example of a configuration ofa fourth embodiment of a compressive encoding apparatus.

FIG. 13 is an explanatory diagram of a second conversion table table2.

FIG. 14 is a block diagram illustrating an example of a configuration ofa fourth embodiment of a decoding apparatus.

FIG. 15 is a block diagram illustrating an example of a configuration ofa fifth embodiment of a compressive encoding apparatus.

FIG. 16 is a block diagram illustrating an example of a configuration ofa fifth embodiment of a decoding apparatus.

FIG. 17 is a block diagram illustrating an example of a configuration ofa sixth embodiment of a compressive encoding apparatus.

FIG. 18 is a block diagram illustrating an example of a configuration ofa sixth embodiment of a decoding apparatus.

FIG. 19 is a block diagram illustrating an example of a configuration ofa seventh embodiment of a compressive encoding apparatus.

FIG. 20 is a block diagram illustrating an example of a configuration ofa seventh embodiment of a decoding apparatus.

FIG. 21 is a block diagram illustrating an example of a configuration ofan eighth embodiment of a compressive encoding apparatus.

FIG. 22 is a block diagram illustrating an example of a configuration ofan eighth embodiment of a decoding apparatus.

FIG. 23 is a block diagram illustrating an example of a configuration ofa ninth embodiment of a compressive encoding apparatus.

FIG. 24 is a block diagram illustrating an example of a configuration ofa ninth embodiment of a decoding apparatus.

FIG. 25 is an explanatory diagram of an example of processing results.

FIG. 26 is a block diagram illustrating an example of a configuration ofa tenth embodiment of a compressive encoding apparatus.

FIG. 27 is a block diagram illustrating an example of a configuration ofa tenth embodiment of a decoding apparatus.

FIG. 28 is an explanatory diagram of the first conversion table table1.

FIG. 29 is an explanatory diagram of the second conversion table table2.

FIG. 30 is a block diagram illustrating an example of a configuration ofan 11th embodiment of a compressive encoding apparatus.

FIG. 31 is a block diagram illustrating an example of a configuration ofan 11th embodiment of a decoding apparatus.

FIG. 32 is an explanatory diagram of an example of processing results.

FIG. 33 is a block diagram illustrating an example of a configuration ofan embodiment of a computer.

MODE(S) FOR CARRYING OUT THE INVENTION

Forms (referred to as embodiments hereinafter) for embodying the presentdisclosure will be described below. A description will be given in thefollowing order.

-   1. First embodiment (basic configuration example)-   2. Second embodiment (configuration example of compressing and    transmitting conversion table data)-   3. Third embodiment (configuration example of selecting from    multiple conversion tables)-   4. Fourth embodiment (configuration example of using two-stage    conversion table)-   5. Fifth embodiment (configuration example of compressing and    transmitting two-stage conversion table)-   6. Sixth embodiment (configuration example of selecting from    multiple two-stage conversion tables)-   7. Seventh embodiment (first configuration example of selecting    multiple past data reference bit numbers)-   8. Eighth embodiment (second configuration example of selecting    multiple past data reference bits numbers)-   9. Ninth embodiment (configuration example of compressing and    transmitting Q-stage conversion table)-   10. Tenth embodiment (first configuration example having 4-to-2    encoding unit and 4-to-1 encoding unit)-   11. Eleventh embodiment (second configuration example having 4-to-2    encoding unit and 4-to-1 encoding unit)    <1. First Embodiment>    <Example of Configuration of Compressive Encoding Apparatus>

FIG. 1 illustrates an example of a configuration of a first embodimentof a compressive encoding apparatus according to the present disclosure.

A compressive encoding apparatus 1 illustrated in FIG. 1 is an apparatuswhich converts an analog audio signal into a digital signal through ΔΣ(sigma delta) modulation, compressively encodes the converted audiosignal and outputs the compressed signal.

The analog audio signal is input from an input unit 11 and supplied toan ADC 12. The ADC 12 digitalizes the supplied analog audio signalthrough ΔΣ modulation and outputs the digital signal to an input buffer13.

The ADC 12 includes an adder 21, an integrator 22, a comparator 23, a1-sample delay circuit 24 and a 1-bit DAC 25.

The audio signal supplied from the input unit 11 is provided to theadder 21. The adder 21 adds an analog audio signal from one sampleperiod before, supplied from the 1-bit DAC 25, to the audio signal fromthe input unit 11 and outputs the added signal to the integrator 22.

The integrator 22 integrates the audio signal from the adder 21 andoutputs the integrated signal to the comparator 23. The comparator 231-bit quantizes the input audio signal for each sample period throughcomparison with a midpoint potential of the input audio signal. As afrequency of the sample period (sampling frequency), 64 or 128 timesconventional 48 kHz and 44.1 kHz are used. The comparator 23 outputs the1-bit quantized audio signal to the input buffer 13 and simultaneouslysupplies the same to the 1-sample delay circuit 24.

The 1-sample delay circuit 24 delays the audio signal from thecomparator 23 by one sample period and outputs the delayed audio signalto the 1-bit DAC 25. The 1-bit DAC 25 converts the digital signal fromthe 1-sample delay circuit 24 into an analog signal and outputs theanalog signal to the adder 21.

The ADC 12 configured as above converts the audio signal supplied fromthe input unit 11 into a 1-bit digital signal (AD conversion) andoutputs the 1-bit digital signal to the input buffer 13. According tosuch AD conversion of ΔΣ modulation, it is possible to obtain a digitalaudio signal which has a wide dynamic range despite having a smallnumber of bits, for example, 1 bit, by sufficiently increasing thefrequency of the sample period (sampling frequency).

In the present embodiment, the ADC 12 receives a stereo (2-channel)audio signal from the input unit 11, AD-converts the stereo audio signalinto a 1-bit signal at a sampling frequency of 128 times 44.1 kHz andoutputs the 1-bit signal to the input buffer 13.

Further, in ΣΔ modulation, the number of quantization bits may be 2 bitsor 4 bits.

The input buffer 13 temporarily accumulates the 1-bit digital audiosignal supplied from the ADC 12 and supplies the 1-bit digital audiosignal in units of one frame to a controller 14, an encoding unit 15 anda data quantity comparison unit 17 at the following stages. Here, oneframe is a unit considered as one of divisions of the audio signal by apredetermined time (period), and in the present embodiment, 3 secondsare regarded as one frame. Accordingly, in other words, the input buffer13 supplies the audio signal in units of 3 seconds to the controller 14,the encoding unit 15 and the data quantity comparison unit 17.

As described above, the audio signal input from the input unit 11 is astereo (2-channel) signal and is AD-converted into a 1-bit signal at thesampling frequency of 128 times 44.1 kHz, and thus the quantity of dataper frame is 44,100 (Hz)*128*2(ch)*3 (sec)=5.6 Mbit.

Hereinafter, a ΔΣ-modulated digital signal supplied from the inputbuffer 13 will be referred to as DSD data.

The controller 14 controls the overall operation of the compressiveencoding apparatus 1. Further, the controller 14 has a function ofcreating a conversion table table1 necessary for the encoding unit 15 toperform compressive encoding and providing the conversion table to theencoding unit 15.

Specifically, the controller 14 creates a data generation count tablepretable using DSD data of one frame supplied from the input buffer 13and further creates a conversion table table1 from the data generationcount table pretable. The controller 14 supplies the created conversiontable table1 to the encoding unit 15 and a data transmission unit 18.The conversion table table1 is created (updated) in units of one frameand supplied to the encoding unit 15.

The encoding unit 15 compressively encodes the DSD data supplied fromthe input buffer 13 in units of 4 bits using the conversion table table1supplied from the controller 14. Accordingly, although the DSD data issupplied to the encoding unit 15 from the input buffer 13 simultaneouslywith timing of supplying to the controller 14, processing is held in theencoding unit 15 until the conversion table is supplied from thecontroller 14.

While details of compressive encoding will be described below withreference to FIG. 2, the encoding unit 15 encodes 4-bit DSD data into2-bit data or 6-bit data and outputs the same to an encoded data buffer16.

The encoded data buffer 16 temporarily buffers the compressed data whichis the DSD data compressively encoded in the encoding unit 15 andsupplies the compressed data to the data quantity comparison unit 17 andthe data transmission unit 18.

The data quantity comparison unit 17 compares the quantity of the DSDdata (also referred to as uncompressed data) supplied from the inputbuffer 13 with the quantity of the compressed data supplied from theencoded data buffer 16 on a frame-by-frame basis. As described above,the encoding unit 15 encodes the 4-bit DSD data into 2-bit data or 6-bitdata and thus there may be a case in which the quantity of data aftercompression exceeds the quantity of data before compression in analgorithm. Accordingly, the data quantity comparison unit 17 comparesthe quantity of the compressed data with the quantity of theuncompressed data, selects the data with the smaller quantity andsupplies selection control data indicating which data has been selectedto the data transmission unit 18. Further, when the data quantitycomparison unit 17 supplies selection control data indicating that theuncompressed data has been selected to the data transmission unit 18,the data quantity comparison unit 17 also supplies the uncompressed datato the data transmission unit 18. The selection control data may be aflag indicating whether audio data transmitted from the datatransmission unit 18 is data compressively encoded in the encoding unit15 from the viewpoint of an apparatus at a receiving side which receivestransmission data.

The data transmission unit 18 selects one of the compressed datasupplied from the encoded data buffer 16 and the uncompressed datasupplied from the data quantity comparison unit 17 on the basis of theselection control data supplied from the data quantity comparison unit17 and transmits the selected data along with the selection control datato a counterpart apparatus through an output unit 19.

In addition, when the data transmission unit 18 transmits the compresseddata, the data transmission unit 18 also adds data of the conversiontable table1 supplied from the controller 14 to the compressed data andtransmits the same to the counterpart apparatus. The data transmissionunit 18 may add a synchronization signal and an error correction code(ECC) to a digital signal corresponding to a predetermined number ofsamples and transmit the same as transmission data.

<Method of Creating Data Generation Count Table>

Next, a method of creating the data generation count table pretable bythe controller 14 will be described.

The controller 14 creates the data generation count table pretable forDSD data of one frame and represents the DSD data supplied from theinput buffer 13 in units of 4 bits as follows.

-   . . . D4 [n−3], D4 [n−2], D4[n−1], D4[n], D4[n+1], D4[n+2], D4[n+3],    . . . .    Here, D4[n] represents continuous 4-bit data and is also referred to    as D4 data hereinafter (n>3).

The controller 14 counts the number of times D4 data is generated afterpast three pieces of D4 data (past 12-bit data) and creates a datageneration count table pretable[4096][16] illustrated in FIG. 2. Here,[4096] and [16] of the data generation count table pretable[4096][16]represent that the data generation count table is a table having 4,096columns and 16 columns (matrix), and columns [0] to [4095] correspond tovalues that may be the past three pieces of D4 data (a past bit pattern)and columns [0] to [15] correspond to values that may be the followingD4 data.

Specifically, pretable[0][0] to [0][15] corresponding to the firstcolumn of the data generation count table pretable indicates the numberof times the following data is generated when the past three pieces ofD4 data D4[n−3], D4[n−2], D4[n−1] were “0”={0000,0000,0000} andrepresents that the number of times the following 4 bits having the pastthree pieces of data of “0” were “0” is 369a (HEX notation) and therewas no other data.

pretable[1][0] to [1][15] corresponding to the second column of the datageneration count table pretable indicates the number of times thefollowing data is generated when the past three pieces of D4 dataD4[n−3], D4[n−2], D4[n−1] were “1”={0000,0000,0001}. When all elementsof the second column of the data generation count table pretable are“0,” this represents that data having three pieces of D4 data as thepast data which was “1” was not present in this one frame.

Further, pretable[117][0] to [117][15] corresponding to the 118^(th)column of the data generation count table pretable indicates the numberof times the following data is generated when the past three pieces ofD4 data D4[n−3], D4[n−2], D4[n−1] were “117”, {0000,0111,0101} in FIG.2. This data represents that the number of times the following 4 bitshaving the past three pieces of data of “117” were 0 is 0, the number oftimes the following 4 bits were “1” is 1, the number of times thefollowing 4 bits were “2” is 10, the number of times the following 4bits were “3” is 18, the number of times the following 4 bits were “4”is 20, the number of times the following 4 bits were “5” is 31, thenumber of times the following 4 bits were “6” is 11, the number of timesthe following 4 bits were “7” is 0, the number of times the following 4bits were “8” is 4, the number of times the following 4 bits were “9” is12, the number of times the following 4 bits were “10” is 5, and thenumber of times the following 4 bits were “11” to “15” is 0.

The controller 14 counts the number of times D4 data is generated afterpast three pieces of D4 data (past 12-bit data) for DSD data of oneframe and creates the data generation count table pretable, as describedabove.

<Method of Creating Conversion Table>

Next, a method of creating the conversion table table1 by the controller15 will be described.

The controller 14 creates a conversion table table1[4096][3] having4,096 columns and 3 columns on the basis of the previously created datageneration count table pretable. Here, columns [0] to [4095] of theconversion table table1[4096][3] correspond to values that may be thepast three pieces of D4 data, and columns [0] to [2] contain threevalues having a high generation frequency from among 16 values that maybe the following D4 data. The first column [0] of the conversion tabletable1[4096][3] contains a (first) value having the highest generationfrequency, the second column [1] contains a value having the secondgeneration frequency, and the third column [2] contains a value havingthe third generation frequency.

FIG. 3 illustrates an example of the conversion table table1[4096][3]corresponding to the data generation count table pretable illustrated inFIG. 2.

table1[117][0] to [117][2] corresponding to the 118^(th) column of theconversion table table1[4096][3] is {05, 04, 03}. This corresponds tothe contents of pretable1[117][0] to [117][15] of the 118^(th) column ofthe data generation count table pretable of FIG. 2.

In pretable[117][0] to [117][15] of the 118^(th) column of the datageneration count table pretable in FIG. 2, a (first) value having thehighest generation frequency is “5” which has been generated 31 times, avalue having the second generation frequency is “4” which has beengenerated 20 times, and a value having the third generation frequency is“3” which has been generated 8 times. Accordingly, {05} is contained inthe 118^(th) column and first column table1[117][0] of the conversiontable table1[4096][3], {04} is contained in the 118^(th) column andsecond column table1[117][1], and {03} is contained in the 118^(th)column and third column table1[117][2].

Similarly, table1[0][0] to [0][2] of the first column of the conversiontable table1[4096][3] corresponds to the contents of pretable[0][0] to[0][15] which is the first column of the data generation count tablepretable of FIG. 2.

In pretable[0][0] to [0][15] of the first column of the data generationcount table pretable of FIG. 2, a (first) value having the highestgeneration frequency is “0” which has been generated 369 a (HEXnotation) times and no other values are generated. Accordingly, {00} iscontained in the first column and first column table1[0][0] of theconversion table table1[4096][3] and {ff} indicating that there is nodata is contained in the first column and second column table [0][1] andthe first column and third column table1[0][2]. The value indicatingthat there is no data is not limited to {ff} and may be appropriatelydecided. Although a value contained in each element of the conversiontable table1 is any of “0” to “15” and thus can be represented by 4bits, the value is represented by 8 bits for facilitation of computerprocessing handling.

As described above, the conversion table table1[4096][3] having 4,096columns and 3 columns is created on the basis of the previously createddata generation count table pretable and supplied to the encoding unit15.

<Compressive Encoding Method Performed by Encoding Unit 15>

Next, a compressive encoding method using the conversion table table1 bythe encoding unit 15 will be described.

For example, a case in which the encoding unit 15 encodes D4[n] fromamong DSD data . . . D4 [n−3], D4 [n−2], D4[n−1], D4[n], D4[n+1],D4[n+2], D4[n+3], . . . supplied from the input buffer 13 will bedescribed.

When D4[n] is encoded, the encoding unit 15 regards D4[n−3], D4[n−2],D4[n−1] which are the past 12-bit data immediately before D4[n] as amass of 12-bit data and searches for three values, table1[D4[n−3],D4[n−2], D4[n−1]][0], table1[D4 [n−3], D4 [n−2], D4[n−1]][1], andtable1[D4 [n−3], D4 [n−2], D4[n−1]][2], of an address (column) indicatedby D4[n−3], D4[n−2], D4[n−1] of the conversion table table1[4096][3].

When any of the three values, table1[D4[n−3], D4[n−2], D4[n−1]][0],table1[D4[n−3], D4[n−2], D4[n−1]][1], and table1[D4[n−3], D4[n−2],D4[n−1]][2], of the address (column) indicated by D4[n−3], D4[n−2],D4[n−1] of the conversion table table1[4096][3] is identical to D4[n],the encoding unit 15 converts D4[n] into 2 bits of “01b” if D4[n] isidentical to table1[D4[n−3], D4[n−2], D4[n−1]][0], converts D4[n] into 2bits of “10b” if D4[n] is identical to table1[D4[n−3], D4[n−2],D4[n−1]][1] and converts D4[n] into 2 bits of “11b” if D4[n] isidentical to table1[D4[n−3], D4[n−2], D4[n−1]][2].

On the other hand, when none of the three values of the address (column)indicated by D4[n−3], D4[n−2], D4[n−1] of the conversion tabletable1[4096][3] is identical to D4[n], the encoding unit 15 adds “00b”before D4[n] such as “00b+D4[n]” to convert D4[n] into 6 bits. Here, bin “01b,” “10b,” “11b” and “00b+D4[n]” represents binary notation.

As described above, the encoding unit 15 converts the 4-bit DSD dataD4[n] into 2-bit data “01b,” “10b” or “11b” or 6-bit data “00b+D4[n]”using the conversion table table1 and outputs the converted data to theencoded data buffer 16.

<Detailed Configuration of Encoding Unit 15>

FIG. 4 illustrates an example of a configuration of the encoding unit 15which performs the aforementioned compressive encoding.

The 4-bit DSD data (e.g., D4[n]) supplied from the input buffer 13 isstored in a register 51 which contains 4 bits. Further, the output ofthe register 51 is connected to an input port 56 a of a selector 55 anda register 52 which contains 12 bits, and the register 52 contains thepast 12-bit data (e.g., D4[n−3], D4[n−2], D4[n−1]) immediately beforethe 4-bit DSD data stored in the register 51.

A conversion table processing unit 53 has the conversion table table1supplied from the controller 14.

The conversion table processing unit 53 checks whether three values,table1[D4 [n−3], D4 [n−2], D4[n−1]][0], table1[D4 [n−3], D4 [n−2],D4[n−1]][1] and table1[D4[n−3], D4[n−2], D4[n−1]][2], of the addressindicated by the 12-bit data (e.g., D4[n−3], D4[n−2], D4[n−1]) containedin the register 52 include the 4-bit data (e.g., D4[n]) contained in theregister 51, and when the three values include the 4-bit data, stores avalue corresponding to the column in which the value identical to the4-bit data is contained, that is, any of “01b,” “10b” and “11b,” in a2-bit register 54. The data stored in the 2-bit register 54 is suppliedto an input port 56 c of the selector 55.

On the other hand, when the three values of the address indicated by the12-bit data (e.g., D4[n−3], D4[n−2], D4[n−1]) contained in the register52 do not include the 4-bit data (e.g., D4[n]) contained in the register51, the conversion table processing unit 53 outputs a signal indicatingthat conversion is not performed (referred to as a no-conversion signalhereinafter) to the selector 55.

The selector 55 selects one of three input ports 56 a to 56 c andoutputs data acquired through the selected input port 56 through anoutput port 57.

The 4-bit DSD data (e.g., D4[n]) stored in the register 51 is suppliedto the input port 56 a, “00b” is supplied to the input port 56 b, andthe converted 2-bit data stored in the register 54 is supplied to theinput port 56 c.

When the no-conversion signal indicating that conversion is notperformed is supplied from the conversion table processing unit 53, theselector 55 selects the input port 56 b to output “00b” through theoutput port 57 and then selects the input port 56 a to output the 4-bitDSD data (e.g., D4[n]) stored in the register 51 through the output port57. Accordingly, the 6 bits “00b+D4[n],” which are output when theconversion table table1 does not include data identical to D4[n], areoutput through the output port 57.

On the other hand, when the no-conversion signal indicating thatconversion is not performed is not supplied (when a conversion signalindicating that conversion has been performed is supplied), the selector55 selects the input port 56 c to output the converted 2-bit datasupplied from the register 54 through the output port 57. Accordingly,the 2 bits output when the conversion table table1 includes dataidentical to D4[n], that is, any of “01b,” “10b” and “11b” is outputthrough the output port 57.

<Compressive Encoding Process Flow>

A compressive encoding process performed by the compressive encodingapparatus 1 will be described with reference to the flowchart of FIG. 5.

The process of the ADC 12 is omitted in the process flow of FIG. 5, anda process after DSD data of one frame, which has been ΔΣ-modulated inthe ADC 12, is output from the input buffer 13 will be described.

First, the controller 14 counts the number of times D4 data is generatedafter the past three pieces of D4 data (past 12-bit data) for DSD dataof one frame and creates the data generation count table pretable instep S1.

The controller 14 creates the conversion table table 1 having 4,096columns and 3 columns on the basis of the created data generation counttable pretable in step S2. The controller 14 supplies the createdconversion table table1 to the encoding unit 15 and the datatransmission unit 18.

The encoding unit 15 executes compressive encoding on the DSD data ofone frame period using the conversion table table1 in step S3.Specifically, the encoding unit 15 performs a process of converting4-bit DSD data D4[n] into 2-bit data “01b,” “10b” or “11b” or 6-bit data“00b+D4[b]” for the DSD data of one frame period. The compressed dataobtained through compressive encoding is supplied to the encoded databuffer 16 and the data quantity comparison unit 17.

The data quantity comparison unit 17 compares the quantity of theuncompressed data of one frame, supplied from the input buffer 13, withthe quantity of the compressed data of one frame, supplied from theencoded data buffer 16, and determines whether the quantity of data hasbeen reduced compared to that before compression in step S4.

When it is determined that the data quantity has been reduced comparedto that before compression in step S4, the process proceeds to step S5and the data quantity comparison unit 17 supplies selection control dataindicating that the compressed data has been selected to the datatransmission unit 18.

In step S6, the data transmission unit 18 adds data of the conversiontable table1 (conversion table data) supplied from the controller 15 tothe selection control data indicating that the compressed data has beenselected (a flag indicating compressively encoded data) and thecompressed data supplied from the encoding unit 15 and transmits thedata to a counterpart apparatus.

On the other hand, when it is determined that the data quantity has notbeen reduced compared to that before compression in step S4, the processproceeds to step S7 and the data quantity comparison unit 17 suppliesthe selection control data indicating that the uncompressed data hasbeen selected along with the uncompressed data to the data transmissionunit 18.

In step S8, the data transmission unit 18 transmits selection controldata indicating that the uncompressed data has been selected (a flagindicating data which has not been compressively encoded) and theuncompressed data to the counterpart apparatus.

In this way, the compressive encoding process of the DSD data of oneframe is completed. The aforementioned process of steps S1 to S8 isrepeated for DSD data in units of one frame sequentially supplied fromthe input buffer 13.

<Example of Configuration of Decoding Apparatus>

FIG. 6 illustrates an example of a configuration of a first embodimentof a decoding apparatus according to the present disclosure.

The decoding apparatus 70 of FIG. 6 is an apparatus for receiving anaudio signal compressively encoded and transmitted by the compressiveencoding apparatus 1 of FIG. 1 and decompressing (reversible decoding)the audio signal.

The audio signal compressively encoded and transmitted by thecompressive encoding apparatus 1 of FIG. 1 is received by an input unit71 of the decoding apparatus 70 through a network which is not shown(e.g., a public line network such as a local area network (LAN), a widearea network (WAN), the Internet, a telephone line network or asatellite communication network) and supplied to a data receiving unit72.

The data receiving unit 72 separates a synchronization signal includedin received data, and detects and corrects a transmission errorgenerated during network transmission.

In addition, the data receiving unit 72 determines whether the audiosignal included in the received data has been compressively encoded onthe basis of selection control data indicating whether the audio signalhas been compressively encoded. When the audio signal has beencompressively encoded, the data receiving unit 72 supplies the receivedcompressed data to an encoded data buffer 73. On the other hand, whenthe audio signal has not been compressively encoded, the data receivingunit 72 supplies the received uncompressed data to an output buffer 76.

Further, the data receiving unit 72 supplies data of the conversiontable table1 (conversion table data) included in the received data to atable storage unit 75. The table storage unit 75 stores the conversiontable table1 supplied from the data receiving unit 72 and supplies theconversion table table1 to a decoding unit 74 as necessary.

The encoded data buffer 73 temporarily accumulates the compressed datasupplied from the data receiving unit 72 and supplies the compresseddata to the following decoding unit 74 at predetermined timing.

The decoding unit 74 decodes (reversibly decodes) the compressed datainto a state before compression and supplies the decoded data to theoutput buffer 76.

The decoding method performed by the decoding unit 74 will be described.

A case in which compressed data which has been compressively encoded andtransmitted by the compressive encoding apparatus 1 is represented inunits of 2 bits as follows and E2[n] is decoded will be described.

-   . . . E2[n−3], E2[n−2], E2[n−1], E2[n], E2[n+1], E2[n+2], E2[n+3], .    . . .    Here, E2[n] represents continuous 2-bit data and is also called E2    data.

First of all, the decoding unit 74 determines the value of E2[n].

When E2[n] is “00b,” this is not data loaded in the received conversiontable table1[4096][3] and thus 4-bit data “E2[n+1]+E2[n+2]” followingE2[n] is data to be decoded.

On the other hand, when E2[n] is “01b,” “10b” or “11b,” this is dataloaded in the received conversion table table1[4096][3] and thus data tobe decoded is searched for with reference to the conversion tabletable1[4096][3] using 12-bit D4 data D4[n−3], D4[n−2], D4[n−1] which hasbeen decoded immediately before E2[n]. The data to be decoded is datacontained in “table1[D4[n−3], D4[n−2], D4[n−1]][E2[n]−1].”

In the above-described manner, the decoding unit 74 can decode(reversibly decode) the compressed data into a state before compression.

The decoding unit 74 includes a 2-bit register 91, a 12-bit register 92,a conversion table processing unit 93, a 4-bit register 94 and aselector 95, as illustrated in FIG. 6.

2-bit E2 data (e.g., E2[n]) supplied from the encoded data buffer 73 isstored in the register 91.

The output of the selector 95 is supplied to the 12-bit register 92 and12-bit data (e.g., D4[n−3], D4[n−2], D4[n−1]), which has been decodedimmediately before the 2-bit E2 data (e.g., E2[n]) stored in theregister 91, is contained in the register 92.

When the 2-bit E2 data (e.g., E2[n]) stored in the register 91 is “00b,”the selector 95 selects an input port 96 a and outputs 4-bit data“E2[n+1]+E2[n+2]” following E2[n] through an output port 97 as adecoding result.

When the 2-bit E2 data (e.g., E2[n]) stored in the register 91 is “01b,”“10b” or “11b,” the conversion table processing unit 93 stores, in theregister 94, 4-bit data contained in “table1[D4[n−3], D4[n−2],D4[n−1]][E2[n]-1]” of the conversion table table1 supplied from thetable storage unit 75. The selector 95 selects an input port 96 b andoutputs the data stored in the register 94 through the output port 97 asa decoding result.

The output buffer 76 appropriately selects one of the uncompressed datasupplied from the data receiving unit 72 and the decoded data suppliedfrom the decoding unit 74 and supplies the selected one to an analogfilter 77.

The analog filter 77 executes predetermined filter processing such aslow pass filter or bandpass filter processing on the decoded datasupplied from the output buffer 76 and outputs the filtered data throughan output unit 78.

<Decoding Process Flow>

The decoding process of the decoding apparatus 700 will be furtherdescribed with reference to the flowchart of FIG. 7.

First, the data receiving unit 72 determines whether received data iscompressively encoded compressed data on the basis of selection controldata included in the received data in step S21.

When it is determined that the received data is compressed data in stepS21, the process proceeds to step S22 and the data receiving unit 72supplies conversion table data included in the received data to thetable storage unit 75. The conversion table processing unit 93 acquiresthe received conversion table table1 through the table storage unit 75.

In addition, the compressed data included in the received data issupplied to the encoded data buffer 73 in step S22.

In step S23, the decoding unit 74 decodes the compressed data suppliedfrom the encoded data buffer 73 using the conversion table table1 andsupplies the decoded data to the output buffer 76. That is, the decodingunit 74 supplies 4-bit data “E2[n+1]+E2[n+2]” following E2[n] to theoutput buffer 76 as a decoding result when 2-bit E2 data (e.g., E2[n])is “00b” and supplies 4-bit data contained in “table1[D4[n−3], D4[n−2],D4[n−1]][E2[n]-1]” of the conversion table table1 to the output buffer76 as a decoding result when the 2-bit E2 data (e.g., E2[n]) is “01b,”“10b” or “11b.”

On the other hand, when it is determined that the received data is notcompressed data, that is, the received data is uncompressed data, instep S21, the process proceeds to step S24 and the data receiving unit72 acquires the uncompressed data included in the received data andsupplies the acquired data to the output buffer 76.

According to the aforementioned process, the uncompressed data or thedata decoded by the decoding unit 74 is supplied to the output buffer 76and the data supplied to the output buffer 76 is output to the analogfilter 77.

In step S25, the analog filter 77 executes predetermined filterprocessing on the data supplied through the output buffer 76. Thefiltering processed audio signal is output through the output unit 78.

The aforementioned process is repeated for audio signals in units of oneframe.

According to the aforementioned first embodiment, the compressiveencoding apparatus 1 compressively encodes and transmits DSD data andthe decoding apparatus 70 receives the compressively encoded andtransmitted data, reversibly decodes the received data and outputs thedecoded data. In the first embodiment, data of the conversion tabletable1 used for compressive encoding is also transmitted as transmissiondata.

<2. Second Embodiment>

<Example of Configuration of Compressive Encoding Apparatus>

FIG. 8 illustrates an example of a configuration of a second embodimentof the compressive encoding apparatus according to the presentdisclosure.

In FIG. 8, same symbols are affixed to parts corresponding to theaforementioned first embodiment and description thereof is appropriatelyomitted. The same applies to other embodiments which will be describedbelow.

In comparison of the compressive encoding apparatus 1 of FIG. 8 with thecompressive encoding apparatus 1 of the first embodiment illustrated inFIG. 1, a conversion table compression unit 101 is newly included inpart of the controller 14 in the compressive encoding apparatus 1 of thesecond embodiment.

The first embodiment employs a configuration in which the conversiontable table1[4096][3] having 4,096 columns and 3 columns created by thecontroller 14 is not compressed as conversion table data but istransmitted along with compressed data. This is because the quantity ofdata of the conversion table table1 having 4,096 columns and 3 columnsis remarkably smaller than 5.6 Mbit data per frame.

However, a case in which the quantity of data of the conversion tabletable1 is greater than the quantity of compressed data may be conceived.In such a case, the conversion table compression unit 101 may beprovided as in the second embodiment. The conversion table compressionunit 101 compresses data of the conversion table table1 by compressingthe data of the conversion table table1 through a predeterminedcompression method, creating differential data of the conversion tabletable1, or the like to create compressed conversion table data andsupplies the compressed conversion table data to the data transmissionunit 18.

The data transmission unit 18 transmits the compressed conversion tabledata instead of the conversion table data in the first embodiment to acounterpart apparatus along with the compressed data.

<Example of Configuration of Decoding Apparatus>

FIG. 9 illustrates an example of a configuration of a second embodimentof a decoding apparatus according to the present disclosure.

The decoding apparatus 70 of FIG. 9 is an apparatus for receiving anaudio signal compressively encoded and transmitted by the compressiveencoding apparatus 1 of FIG. 8 and decompressing (reversible decoding)the audio signal.

In comparison of the decoding apparatus 70 of FIG. 9 with the decodingapparatus 70 of the first embodiment illustrated in FIG. 6, a conversiontable decompression unit 111 is newly provided between the datareceiving unit 72 and the table storage unit 75 in the decodingapparatus 70 of the second embodiment.

The conversion table decompression unit 111 executes a decompressionprocess corresponding to the compression process performed by theconversion table compression unit 101 of FIG. 8 on compressed conversiontable data supplied from the data receiving unit 72. The conversiontable table1 acquired as a result of the decompression process issupplied to the table storage unit 75 as in the first embodiment.

According to the aforementioned second embodiment, the compressiveencoding apparatus 1 compressively encodes and transmits DSD data andthe decoding apparatus 70 receives the compressively encoded andtransmitted data, reversibly decodes the received data and outputs thedecoded data. In the second embodiment, the data of the conversion tabletable1 used for compressive encoding is compressed and transmitted astransmission data.

<3. Third Embodiment>

<Example of Configuration of Compressive Encoding Apparatus>

FIG. 10 illustrates an example of a configuration of a third embodimentof the compressive encoding apparatus according to the presentdisclosure.

In comparison of the compressive encoding apparatus 1 of FIG. 10 withthe compressive encoding apparatus 1 of the first embodiment illustratedin FIG. 1, a plurality of conversion tables table1 are provided in thecontroller 14 in the compressive encoding apparatus 1 of the thirdembodiment. Although the controller 14 stores three types of conversiontables table1, conversion table table1-1, conversion table table1-2 andconversion table table1-3, in the present embodiment, the number ofconversion tables table1 included in the controller 14 is not limited.

The conversion table table1 created on the basis of the data generationcount table pretable has little difference among content. This isbecause there is no large difference in patterns having high generationfrequencies even though the order of generation frequency slightlychanges.

Accordingly, it is possible to previously create a plurality of types ofconversion tables table1 using a plurality of pieces of content, storethe conversion tables table1 in the controller 14, appropriately selectconversion tables and perform compressive encoding, as illustrated inFIG. 10. The controller 14 serves as a storage unit which stores thepreviously created plurality of types of conversion tables table1.

When the quantity of data of the conversion table table1 cannot beignorable even though the data of the conversion table table1 has beencompressed, as in the aforementioned second embodiment, or theconversion table table1 cannot be transmitted for some reasons such asbalancing of communication lines, it is possible to employ aconfiguration in which compressive encoding is performed using theplurality of types of conversion tables table1 previously stored in thecontroller 14, as in the present embodiment.

Further, there is a case in which the ADC 12 that performs ΔΣ modulationhas different characteristics depending on makers which provide the ADC12, and the like. Accordingly, the plurality of conversion tables table1stored in the controller 14 may correspond to a maker which provides theADC 12.

The plurality of conversion tables table1 previously stored in thecontroller 14 are commonly included in an apparatus of a decoding side.

Therefore, the conversion table table1 of transmission content iscreated in units of one frame and transmitted in real time in theaforementioned first and second embodiments, whereas the conversiontable table1 of transmission content need not be created in the thirdembodiment.

The controller 14 selects a conversion table table1 most suitable forDSD data supplied from the input buffer 13 from the previously storedplurality of conversion tables table1 and supplies conversion tabledesignation data which designates the selected conversion table table1to the data transmission unit 18.

The data transmission unit 18 transmits the conversion table designationdata instead of the conversion table data in the first embodiment to acounterpart apparatus along with compressed data and the like.

The controller 14 checks compression rates of the plurality ofconversion tables table1 by sequentially supplying the plurality ofconversion tables table1 included therein to the encoding unit 15 tocompressively encode the conversion tables table1. Then, the controller14 supplies a conversion table table1 having a highest compression rateto the encoding unit 15 as a conversion table table1 to be used andsupplies conversion table designation data which designates the selectedconversion table table1 to the data transmission unit 18.

Further, the controller 14 may have the same encoding function as theencoding unit 15, compressively encode DSD data supplied from the inputbuffer 13 with the plurality of conversion tables table1 includedtherein and decide the conversion table table1 having the highestcompression rate, for example.

In addition, with respect to timing of selecting one of the plurality ofconversion tables table1, one of the plurality of conversion tablestable1 may be selected frame by frame or content by content. That is,compressive encoding may be performed using all conversion tables table1only in the first frame of transmitted content and, when a conversiontable table1 having a highest compression rate is decided, compressiveencoding may be performed using the same conversion table table1 for thecontent, or compressive encoding may be performed using all conversiontables table1 in units of one frame or several frames every time and aconversion table table1 having a highest compression rate may bedecided.

<Example of Configuration of Decoding Apparatus>

FIG. 11 illustrates an example of a configuration of a third embodimentof a decoding apparatus according to the present disclosure.

The decoding apparatus 70 of FIG. 11 is an apparatus for receiving anaudio signal compressively encoded and transmitted by the compressiveencoding apparatus 1 of FIG. 10 and decompressing (reversible decoding)the audio signal.

In comparison of the decoding apparatus 70 of FIG. 11 with the decodingapparatus 70 of the first embodiment illustrated in FIG. 6, a pluralityof conversion tables (conversion table table1-1, conversion tabletable1-2 and conversion table table1-3) identical to those stored in thecontroller 14 of the compressive encoding apparatus 1 of FIG. 10 arestored in the table storage unit 75 in the decoding apparatus 70 of thethird embodiment.

The data receiving unit 72 supplies conversion table designation dataincluded in received data to the table storage unit 75. The tablestorage unit 75 supplies the conversion table table1 (one of theconversion table table1-1, conversion table table1-2 and conversiontable table1-3) designated by the conversion table designation datasupplied from the data receiving unit 72 to the decoding unit 74.

According to the aforementioned third embodiment, the compressiveencoding apparatus 1 compressively encodes and transmits DSD data andthe decoding apparatus 70 receives the compressively encoded andtransmitted data, reversibly decodes the received data and outputs thedecoded data. In the third embodiment, conversion tables table1 used forcompressive encoding are previously stored.

<4. Fourth Embodiment>

<Example of Configuration of Compressive Encoding Apparatus>

FIG. 12 illustrates an example of a configuration of a fourth embodimentof the compressive encoding apparatus according to the presentdisclosure.

In comparison of the compressive encoding apparatus 1 of FIG. 12 withthe compressive encoding apparatus 1 of the first embodiment illustratedin FIG. 1, the compressive encoding apparatus 1 of the fourth embodimentdiffers from the compressive encoding apparatus 1 of the firstembodiment in that the controller 14 also creates a second conversiontable table2 in addition to a first conversion table table1 identical tothe conversion table table1. The controller 14 supplies the createdfirst conversion table table1 and second conversion table table2 to theencoding unit 15 and the data transmission unit 18. In the following,the first conversion table table1 and the second conversion table table2are integrated and called a 2-stage conversion table table.

That is, in the aforementioned first embodiment, the compressiveencoding apparatus 1 stores ranked three values having higher generationfrequencies from the data generation count table pretable in theconversion table table1 and adds D4 data behind “00b” as it is andtransmits 6 bits for other values.

In the fourth embodiment, the second conversion table table2 whichcontains values having fourth to sixth highest generation frequencies isfurther created from the data generation count table pretable inaddition to the first conversion table table1.

FIG. 13 illustrates an example of a second conversion tabletable2[4096][3] created from the data generation count table pretableillustrated in FIG. 2.

In pretable[117][0] to [117][15] of the 118^(th) column of the datageneration count table pretable in FIG. 2, a value having the fourthgeneration frequency is “9” which has been generated 12 times, a valuehaving the fifth generation frequency is “6” which has been generated 11times, and a value having the sixth generation frequency is “2” whichhas been generated 10 times.

Accordingly, {09} is contained in the 118^(th) column and first columntable1[117][0] of the second conversion table table2[4096][3]illustrated in FIG. 13, {06} is contained in the 118^(th) column andsecond column table1[117][1], and {02} is contained in the 118^(th)column and third column table1[117][2].

<Compressive Encoding Method Using First Conversion Table Table1 andSecond Conversion Table Table2>

A compressive encoding method using the first conversion table table1and the second conversion table table2 by the encoding unit 15 of thefourth embodiment will be described.

In a way similar to the first embodiment, a case in which the encodingunit 15 encodes D4[n] from among DSD data . . . D4 [n−3], D4 [n−2],D4[n−1], D4[n], D4[n+1], D4[n+2], D4[n+3], . . . supplied from the inputbuffer 13 will be described.

When D4[n] is encoded, the encoding unit 15 regards D4[n−3], D4[n−2],D4[n−1] which are the past 12-bit data immediately before D4[n] as amass of 12-bit data and searches for three values, table1[D4[n−3],D4[n−2], D4[n−1]][0], table1[D4 [n−3], D4 [n−2], D4[n−1]][1], andtable1[D4 [n−3], D4 [n−2], D4[n−1]][2], of an address (column) indicatedby D4[n−3], D4[n−2], D4[n−1] of the first conversion tabletable1[4096][3].

When any of the three values, table1[D4[n−3], D4[n−2], D4[n−1]][0],table1[D4[n−3], D4[n−2], D4[n−1]][1], and table1[D4[n−3], D4[n−2],D4[n−1]][2], of the address (column) indicated by D4[n−3], D4[n−2],D4[n−1] is identical to D4[n], the encoding unit 15 converts D4[n] into2 bits of “01b” if D4[n] is identical to table1[D4[n−3], D4[n−2],D4[n−1]][0], converts D4[n] into 2 bits of “10b” if D4[n] is identicalto table1[D4[n−3], D4[n−2], D4[n−1]][1] and converts D4[n] into 2 bitsof “11b” if D4[n] is identical to table1[D4[n−3], D4[n−2], D4[n−1]][2].

On the other hand, when the three values of the address (column)indicated by D4[n−3], D4[n−2]D4[n−1] of the first conversion tabletable1[4096][3] do not include data identical to D4[n], the encodingunit 15 searches for three values, table2[D4[n−3], D4[n−2], D4[n−1]][0],table2[D4[n−3], D4[n−2], D4[n−1]][1] and table2[D4[n−3], D4[n−2],D4[n−1]][2], of the address (column) indicated by D4[n−3],D4[n−2]D4[n−1] of the second conversion table table2[4096][3].

When any of the three values, table2[D4[n−3], D4[n−2], D4[n−1]][0],table2[D4[n−3], D4[n−2], D4[n−1]][1], and table2[D4[n−3], D4[n−2],D4[n−1]][2], of the address (column) indicated by D4[n−3], D4[n−2],D4[n−1] of the second conversion table table2[4096][3] is identical toD4[n], the encoding unit 15 converts D4[n] into 4 bits of “0001b” ifD4[n] is identical to table2[D4[n−3], D4[n−2], D4[n−1]][0], convertsD4[n] into 4 bits of “0010b” if D4[n] is identical to table2[D4[n−3],D4[n−2], D4[n−1]][1] and converts D4[n] into 4 bits of “0011b” if D4[n]is identical to table2[D4[n−3], D4[n−2], D4[n−1]][2].

On the other hand, when the three values of the address (column)indicated by D4[n−3], D4[n−2]D4[n−1] of the second conversion tabletable2[4096][3] do not include data identical to D4[n], the encodingunit 15 adds “0000b” before D4[n], such as “000b+D4[n],” to convertD4[n] into 8 bits. Here, b in “0001b,” “0010b,” “0011b” and“0000b+D4[n]” represents binary notation.

As described above, the encoding unit 15 can compressively encode DSDdata supplied from the input buffer 13 using both the first conversiontable table1 and the second conversion table table2.

The data quantity comparison unit 17 compares the quantity of the DSDdata supplied from the input buffer 13 with the quantity of compresseddata which has been compressively encoded using both the firstconversion table table1 and the second conversion table table2 and issupplied from the encoded data buffer 16, selects data in the smallerquantity and supplies selection control data indicating the selecteddata to the data transmission unit 18.

Further, the encoding unit 15 may, of course, compressively encode DSDdata using only the first conversion table table1 among the firstconversion table table1 and the second conversion table table2.

Accordingly, the controller 14 checks compression rates of compressiveencoding using only the first conversion table table1 and compressiveencoding using both the first conversion table table1 and the secondconversion table table2. Then, the controller 14 may supply compressiveencoding having a higher compression rate to the encoding unit 15 as aconversion table table to be used and supply the same to the datatransmission unit 18.

<Example of Configuration of Decoding Apparatus>

FIG. 14 illustrates an example of a configuration of a fourth embodimentof a decoding apparatus according to the present disclosure.

The decoding apparatus 70 of FIG. 14 is an apparatus which receives anaudio signal compressively encoded and transmitted by the compressiveencoding apparatus 1 of FIG. 12 and decompresses (reversibly decodes)the received audio signal.

In comparison of the decoding apparatus 70 of FIG. 14 with the decodingapparatus 70 of the first embodiment illustrated in FIG. 6, the decodingapparatus 70 of the fourth embodiment differs from the decodingapparatus 70 of the first embodiment in that both the first conversiontable table1 and the second conversion table table2 transmitted from thecompressive encoding apparatus 1 of FIG. 12 are stored in the tablestorage unit 75.

A description will be given of a decoding method using the firstconversion table table1 and the second conversion table table2, which isperformed by the decoding unit 74 of the fourth embodiment.

A description will be given of case in which compressed data which hasbeen compressively encoded and transmitted by the compressive encodingapparatus 1 is . . . E2[n−3], E2[n−2], E2[n−1], E2[n], E2[n+1], E2[n+2],E2[n+3], . . . and E2[n] is decoded.

First of all, the decoding unit 74 determines the value of E2[n].

When E2[n] is “00b,” this is not data loaded in the received firstconversion table table1[4096][3], and thus the decoding unit 74determines the value of E2[n+1].

When E2[n+1] is also “00b,” this is not data loaded in the receivedsecond conversion table table2[4096][3], and thus 4-bit data“E2[n+2]+E2[n+3]” following E2[n+1] is data to be decoded.

On the other hand, when E2[n+1] is “01b,” “10b” or “11b,” this is dataloaded in the received second conversion table table2[4096][3] and thusdata to be decoded is searched for with reference to the secondconversion table table2[4096][3] using 12-bit D4 data D4[n−3], D4[n−2],D4[n−1] which has been decoded immediately before E2[n]. The data to bedecoded is data contained in “table2[D4[n−3], D4[n−2],D4[n−1]][E2[n+1]−1].”

On the other hand, when E2[n] is “01b,” “10b” or “11b,” this is dataloaded in the received first conversion table table1[4096][3] and thusdata to be decoded is searched for with reference to the firstconversion table table1[4096][3] using 12-bit D4 data D4[n−3], D4[n−2],D4[n−1] which has been decoded immediately before E2[n]. The data to bedecoded is data contained in “table1[D4[n−3], D4[n−2],D4[n−1]][E2[n]−1].”

As described above, the decoding unit 74 can decode (reversibly decode)compressed data into a state before compression using the firstconversion table table1 and the second conversion table table2.

According to the aforementioned forth embodiment, the compressiveencoding apparatus 1 compressively encodes and transmits DSD data andthe decoding apparatus 70 receives the compressively encoded andtransmitted data, reversibly decodes the received data and outputs thedecoded data. In the fourth embodiment, the first conversion tabletable1 and the second conversion table table2 used for compressiveencoding are transmitted as transmission data.

<5. Fifth Embodiment>

<Example of Configuration of Compressive Encoding Apparatus>

FIG. 15 illustrates an example of a configuration of a fifth embodimentof the compressive encoding apparatus according to the presentdisclosure.

The compressive encoding apparatus 1 of the fifth embodiment illustratedin FIG. 15 has a configuration obtained by adding the configuration ofthe conversion table compression unit 101 of the second embodimentillustrated in FIG. 8 to the compressive encoding apparatus 1 of thefourth embodiment illustrated in FIG. 12.

That is, in the compressive encoding apparatus of the fifth embodiment,the controller 14 creates the first conversion table table1 and thesecond conversion table table2 from DSD data of one frame as in theaforementioned fourth embodiment. The conversion table compression unit101 compresses data of the first conversion table table1 and the secondconversion table table2 to create compressed conversion table data andsupplies the compressed conversion table data to the data transmissionunit 18.

<Example of Configuration of Decoding Apparatus>

FIG. 16 illustrates an example of a configuration of a fifth embodimentof a decoding apparatus according to the present disclosure.

The decoding apparatus 70 of FIG. 16 is an apparatus for receiving anaudio signal compressively encoded and transmitted by the compressiveencoding apparatus 1 of FIG. 15 and decompressing (reversible decoding)the audio signal.

The conversion table decompression unit 111 executes a decompressionprocess corresponding to the compression process performed by theconversion table compression unit 101 of FIG. 15 on the compressedconversion table data supplied from the data receiving unit 72. Thefirst conversion table table1 and the second conversion table table2 areacquired through the decompression process. The acquired firstconversion table table1 and second conversion table table2 are suppliedto the table storage unit 75 and used for the decoding process performedby the decoding unit 74 as described in the fourth embodiment.

According to the aforementioned fifth embodiment, the compressiveencoding apparatus 1 compressively encodes and transmits DSD data andthe decoding apparatus 70 receives the compressively encoded andtransmitted data, reversibly decodes the received data and outputs thedecoded data. In the fifth embodiment, the first conversion table table1and the second conversion table table2 used for compressive encoding arecompressed and transmitted as transmission data.

<6. Sixth Embodiment>

<Example of Configuration of Compressive Encoding Apparatus>

FIG. 17 illustrates an example of a configuration of a sixth embodimentof the compressive encoding apparatus according to the presentdisclosure.

The compressive encoding apparatus 1 of the sixth embodiment illustratedin FIG. 17 has a configuration in which a plurality of types of theconfiguration of a 2-stage conversion table of the first conversiontable table1 and the second conversion table table2 employed by thecompressive encoding apparatus 1 of the fourth embodiment illustrated inFIG. 12 are previously created and stored.

That is, in the compressive encoding apparatus 1 of the sixthembodiment, the controller 14 previously stores three types of 2-stageconversion tables table, specifically, a first conversion table table1-1and a second conversion table table2-1, a first conversion tabletable1-2 and a second conversion table table2-2, and a first conversiontable 1-3 and a second conversion table table2-3.

The controller 14 selects a 2-stage conversion table table most suitablefor DSD data supplied from the input buffer 13, that is, a 2-stageconversion table table having a highest compression rate, from thepreviously stored three types of 2-stage conversion tables table. Then,the controller 14 supplies conversion table designation data whichdesignates the selected 2-stage conversion table table to the datatransmission unit 18.

In addition, even when only the three types of first conversion tablestable1 are used, it is possible to decide a first-stage conversion tabletable1 to be used by comparing compression rates, as described in thefourth embodiment.

<Example of Configuration of Decoding Apparatus>

FIG. 18 illustrates an example of a configuration of a sixth embodimentof a decoding apparatus according to the present disclosure.

The decoding apparatus 70 of FIG. 18 is an apparatus for receiving anaudio signal compressively encoded and transmitted by the compressiveencoding apparatus 1 of FIG. 17 and decompressing (reversible decoding)the audio signal.

In the decoding apparatus 70 of the sixth embodiment, three types of2-stage conversion tables table identical to those included in thecontroller 14 of the compressive encoding apparatus 1 of FIG. 17 arepreviously stored in the table storage unit 75. That is, the tablestorage unit 75 previously stores the first conversion table table1-1and the second conversion table table2-1, the first conversion tabletable1-2 and the second conversion table table2-2, and the firstconversion table 1-3 and the second conversion table table2-3.

The data receiving unit 72 supplies conversion table designation dataincluded in received data to the table storage unit 75. The tablestorage unit 75 supplies, to the decoding unit 74, a first-stageconversion table table or a second-stage conversion table tableindicated by the conversion table designation data supplied from thedata receiving unit 72.

According to the aforementioned sixth embodiment, the compressiveencoding apparatus 1 compressively encodes and transmits DSD data andthe decoding apparatus 70 receives the compressively encoded andtransmitted data, reversibly decodes the received data and outputs thedecoded data. In the sixth embodiment, the first conversion table table1and the second conversion table table2 used for compressive encoding arepreviously stored.

<7. Seventh Embodiment>

<Example of Configuration of Compressive Encoding Apparatus>

FIG. 19 illustrates an example of a configuration of a seventhembodiment of the compressive encoding apparatus according to thepresent disclosure.

In the seventh embodiment illustrated in FIG. 19, the configuration ofthe controller 14 is the same as the fifth embodiment illustrated inFIG. 15. That is, the controller 14 creates the 2-stage conversion tabletable of the first conversion table table1 and the second conversiontable table2 from DSD data of one frame. The conversion tablecompression unit 101 compresses data of the created first conversiontable table1 and second conversion table table2 to create compressedconversion table data and supplies the compressed conversion table datato the data transmission unit 18.

Further, the compressive encoding apparatus 1 of the seventh embodimentdiffers from the fifth embodiment illustrated in FIG. 15 in that theencoding unit 15 includes a 12-bit reference encoding unit 141, a 16-bitreference encoding unit 142 and a 20-bit reference encoding unit 143.

The 12-bit reference encoding unit 141 regards past 12-bit data,D4[n−3], D4[n−2], D4[n−1], immediately before D4[n] as a mass of 12-bitdata and encodes D4[n] as in compressive encoding performed by theencoding unit 15 of the aforementioned first to sixth embodiments.

The 16-bit reference encoding unit 142 regards past 16-bit dataimmediately before D4[n] as a mass of 16-bit data and encodes D4[n].

The 20-bit reference encoding unit 143 regards past 20-bit dataimmediately before D4[n] as a mass of 20-bit data and encodes D4[n].

Compressive encoding methods of the 16-bit reference encoding unit 142and the 20-bit reference encoding unit 143 are the same as that of the12-bit reference encoding unit 141 except that the number of bits ofpast data referred to when D4[n] is encoded is different.

There is a case in which a data compression rate can be further improvedby increasing the number of reference bits of past data to 16 bits or 20bits instead of 12 bits. However, when the number of reference bits ofthe past data increases, the quantity of data of a created conversiontable table exponentially increases with respect to the number ofreference bits of the past data. Specifically, although the number ofpatterns of past data is 2¹²=4,096 patterns when the number of referencebits of the pas data is 12, the number of patterns of the past data is2¹⁶=65,536 patterns when the number of reference bits of the pas data is16 and the number of patterns of the past data is 2²⁰=1,048,576 patternswhen the number of reference bits of the pas data is 20.

Accordingly, the controller 14 may decide which one of the 12-bitreference encoding unit 141, the 16-bit reference encoding unit 142 andthe 20-bit reference encoding unit 143 will be used depending on a stateof a communication line, such as traffic of a network interposed betweenthe apparatus and a counterpart apparatus in addition to deciding bychecking compression rates. Further, the decision may be performeddepending on a request from the counterpart apparatus.

<Example of Configuration of Decoding Apparatus>

FIG. 20 illustrates an example of a configuration of a seventhembodiment of a decoding apparatus according to the present disclosure.

The decoding apparatus 70 of FIG. 20 is an apparatus for receiving anaudio signal compressively encoded and transmitted by the compressiveencoding apparatus 1 of FIG. 19 and decompressing (reversible decoding)the audio signal.

The decoding apparatus 70 of the seventh embodiment has the decodingunit 74 corresponding to the 12-bit reference encoding unit 141, the16-bit reference encoding unit 142 and the 20-bit reference encodingunit 143 of the compressive encoding apparatus 1 of FIG. 19. That is,the decoding unit 74 includes a 12-bit reference decoding unit 161, a16-bit reference decoding unit 162 and a 20-bit reference decoding unit163.

In the compressive encoding apparatus 1 of FIG. 19, data of a 2-stageconversion table table (conversion table data) used for compressiveencoding of DSD data is received through the data receiving unit 72,decompressed by the conversion table decompression unit 111 and storedin the table storage unit 75.

The table storage unit 75 supplies the 2-stage conversion table tablesupplied from the conversion table decompression unit 111 to thedecoding unit 74.

In the decoding unit 74, one of the 12-bit reference decoding unit 161,the 16-bit reference decoding unit 162 and the 20-bit reference decodingunit 163 executes a decoding process on the basis of the 2-stageconversion table table supplied from the table storage unit 75. Sincethe number of reference bits of past data can be known according to adata quantity difference in the 2-stage conversion table, a decodingunit which is most suitable for the decoding process is uniquelydecided.

According to the aforementioned seventh embodiment, the compressiveencoding apparatus 1 compressively encodes and transmits DSD data andthe decoding apparatus 70 receives the compressively encoded andtransmitted data, reversibly decodes the received data and outputs thedecoded data. In the seventh embodiment, one of 12 bits, 16 bits and 20bits is selected as the number of reference bits of past data to performcompressive encoding, and the data of the 2-stage conversion table tableused for compressive encoding is compressed and transmitted.

<8. Eighth Embodiment>

<Example of Configuration of Compressive Encoding Apparatus>

FIG. 21 illustrates an example of a configuration of an eighthembodiment of the compressive encoding apparatus according to thepresent disclosure.

In the eighth embodiment illustrated in FIG. 21, the encoding unit 15includes the 12-bit reference encoding unit 141, the 16-bit referenceencoding unit 142 and the 20-bit reference encoding unit 143 as in theseventh embodiment illustrated in FIG. 19.

The controller 14 previously stores a 12-bit 2-stage conversion tabletable used for encoding performed by the 12-bit reference encoding unit141, a 16-bit 2-stage conversion table table used for encoding performedby the 16-bit reference encoding unit 142, and a 20-bit 2-stageconversion table table used for encoding performed by the 20-bitreference encoding unit 143.

That is, while the compressive encoding apparatus 1 in the eighthembodiment has a configuration in which one of 12 bits, 16 bits and 20bits may be selected as the number of reference bits of past data as inthe seventh embodiment, 2-stage conversion tables table are not createdusing transmitted DSD data but are previously stored as in the sixthembodiment illustrated in FIG. 17.

The controller 14 selects a 2-stage conversion table table most suitablefor DSD data supplied from the input buffer 13, that is, a 2-stageconversion table table having a highest compression rate, from a totalof nine types (the number of reference bits of 3 types×3 types perreference bit number) of 2-stage conversion tables table previouslystored therein. Meanwhile, in selection of a most suitable 2-stageconversion table table, compressive encoding may be performed using allthe nine types of 2-stage conversion tables and compression rates may becompared, or a predetermined 2-stage conversion table table may beextracted from reference bits as a representative 2-stage conversiontable and compression rates of reference bit numbers may be compared.

The controller 14 supplies conversion table designation data whichdesignates the selected 2-stage conversion table table to the datatransmission unit 18.

<Example of Configuration of Decoding Apparatus>

FIG. 22 illustrates an example of a configuration of an eighthembodiment of a decoding apparatus according to the present disclosure.

The decoding apparatus 70 of FIG. 22 is an apparatus for receiving anaudio signal compressively encoded and transmitted by the compressiveencoding apparatus 1 of FIG. 21 and decompressing (reversible decoding)the audio signal.

The decoding unit 74 includes the 12-bit reference decoding unit 161,the 16-bit reference decoding unit 162 and the 20-bit reference decodingunit 163 corresponding to the 12-bit reference encoding unit 141, the16-bit reference encoding unit 142 and the 20-bit reference encodingunit 143 of the compressive encoding apparatus 1 of FIG. 21.

The table storage unit 75 previously stores three types of 2-stageconversion tables table identical to those included in the controller 14of the compressive encoding apparatus 1 of FIG. 21, that is, the 12-bit2-stage conversion table table, the 16-bit 2-stage conversion tabletable and the 20-bit 2-stage conversion table table.

The data receiving unit 72 supplies conversion table designation dataincluded in received data to the table storage unit 75. The tablestorage unit 75 supplies, to the decoding unit 74, a second-stageconversion table table indicated by the conversion table designationdata supplied from the data receiving unit 72.

The decoding unit 74 executes a decoding process using one of the 12-bitreference decoding unit 161, the 16-bit reference decoding unit 162 andthe 20-bit reference decoding unit 163 on the basis of the 2-stageconversion tables table supplied from the table storage unit 75.

According to the aforementioned eighth embodiment, the compressiveencoding apparatus 1 compressively encodes and transmits DSD data andthe decoding apparatus 70 receives the compressively encoded andtransmitted data, reversibly decodes the received data and outputs thedecoded data. In the eighth embodiment, one of 12 bits, 16 bits and 20bits is selected as the number of reference bits of past data to performcompressive encoding, and the data of the 2-stage conversion table tableused for compressive encoding is stored in advance.

<9. Ninth Embodiment>

<Example of Configuration of Compressive Encoding Apparatus>

FIG. 23 illustrates an example of a configuration of a ninth embodimentof the compressive encoding apparatus according to the presentdisclosure.

The compressive encoding apparatus 1 of the aforementioned first tothird embodiments has the configuration in which compressing encoding isperformed using a first-stage conversion table table1.

The compressive encoding apparatus 1 of the aforementioned fourth toeighth embodiments has the configuration in which compressive encodingis performed using a 2-stage conversion table table of the firstconversion table table1 and the second conversion table table2.

The compressive encoding apparatus 1 of the ninth embodiment illustratedin FIG. 23 has an exemplary configuration in which compressive encodingis performed using a Q-stage conversion table table (Q being an integergreater than 2) which is a conversion table having 3 or more stages.

As illustrated in FIG. 23, the controller 14 creates the Q-stageconversion table table of a first to Q-th conversion tables table1 totableQ and supplies the Q-stage conversion table table to the encodingunit 15. The encoding unit 15 compressively encodes DSD data suppliedfrom the input buffer 13 in units of 4 bits using the Q-stage conversiontable table supplied from the controller 14.

Here, the conversion unit is 4 bits and three conversion tables tableare created (registered) in descending order of generation frequencyfrom the first conversion table table1, and thus a maximum value of Q is5 in the present embodiment.

Accordingly, a configuration of compressive encoding of creating firstto third conversion tables table1 to table3, a configuration ofcompressive encoding of creating first to fourth conversion tablestable1 to table4, and a configuration of compressive encoding ofcreating first to fifth conversion tables table1 to table5 are conceivedas the ninth embodiment.

When the first to fifth conversion tables table1 to table5 are created,values corresponding to first to third generation frequencies arecontained in the first conversion table table1, values corresponding tofourth to sixth generation frequencies are contained in the secondconversion table table2, values corresponding to seventh to ninthgeneration frequencies are contained in the third conversion tabletable3, values corresponding to tenth to twelfth generation frequenciesare contained in the fourth conversion table table4, and valuescorresponding to thirteenth to fifteenth generation frequencies arecontained in the fifth conversion table table5.

<Example of Configuration of Decoding Apparatus>

FIG. 24 illustrates an example of a configuration of a ninth embodimentof a decoding apparatus according to the present disclosure.

The decoding apparatus 70 of FIG. 24 is an apparatus for receiving anaudio signal compressively encoded and transmitted by the compressiveencoding apparatus 1 of FIG. 23 and decompressing (reversible decoding)the audio signal.

The table storage unit 75 supplies, to the decoding unit 74, the firstconversion table table1 to the Q-th conversion table tableQ that havebeen received by the data receiving unit 72 and decompressed by theconversion table decompression unit 111. The decoding unit 74 performsdecoding using the first conversion table table1 to the Q-th conversiontable tableQ.

<Compressive Encoding Method Using 3-stage Conversion Table Table>

A compressive encoding method using first to third conversion tablestable1 to table3 will be described.

In a way similar to the first embodiment, a case in which the encodingunit 15 encodes D4[n] from among DSD data . . . D4 [n−3], D4 [n−2],D4[n−1], D4[n], D4[n+1], D4[n+2], D4[n+3], . . . supplied from the inputbuffer 13 will be described.

The part of finding a value identical to D4[n] through the firstconversion table table1 to the second conversion table table2 is thesame as that in the compressive encoding method using a 2-stageconversion table table described in the fourth embodiment.

That is, the encoding unit 15 searches the first conversion tabletable1[4096][3] and the second conversion table table2[4096][3] for avalue identical to D4[n], converts D4[n] into 2 bits of “01b,” “10b” or“11b” when the first conversion table table1[4096][3] includes a valueidentical to D4[n] and converts D4[n] into 4 bits of “0001b,” “0010b” or“0011b” when the second conversion table table2[4096][3] includes avalue identical to D4[n].

Subsequently, when the three values of the address (column) indicated byD4[n−3], D4[n−2]D4[n−1] of the second conversion table table2[4096][3]do not include data identical to D4[n], the encoding unit 15 searchesfor three values, table3[D4 [n−3], D4 [n−2], D4[n−1]][0], table3[D4[n−3], D4 [n−2], D4[n−1]][1] and table3[D4[n−3], D4[n−2], D4[n−1]][2],of the address (column) indicated by D4[n−3], D4[n−2]D4[n−1] of thethird conversion table table3[4096][3].

When any of the three values, table3[D4[n−3], D4[n−2], D4[n−1]][0],table3[D4[n−3], D4[n−2], D4[n−1]][1], and table3[D4[n−3], D4[n−2],D4[n−1]][2], of the address (column) indicated by D4[n−3], D4[n−2],D4[n−1] of the third conversion table table3[4096][3] is identical toD4[n], the encoding unit 15 converts D4[n] into 6 bits of “000001b” ifD4[n] is identical to table3[D4[n−3], D4[n−2], D4[n−1]][0], convertsD4[n] into 6 bits of “000010b” if D4[n] is identical to table3[D4[n−3],D4[n−2], D4[n−1]][1] and converts D4[n] into 6 bits of “000011b” ifD4[n] is identical to table3[D4 [n−3], D4 [n−2], D4 [n−1]][2].

On the other hand, when three values of an address (column) indicated byD4[n−3], D4[n−2], D4[n−1] of the third conversion table table3[4096][3]do not include a value identical to D4[n], the encoding unit 15 convertsD4[n] to 10 bits by adding “000000b” before D4[n], such as“000000b+D4[n].”

<Decoding Method Using 3-stage Conversion Table Table>

Next, a decoding method using the first to third conversion tablestable1 to table3 will be described.

A description will be given of case in which compressed data which hasbeen compressively encoded and transmitted by the compressive encodingapparatus 1 is . . . E2[n−3], E2[n−2], E2[n−1], E2[n], E2[n+1], E2[n+2],E2[n+3], . . . and E2[n] is decoded.

When E2[n] is “01b,” “10b” or “11b,” the decoding unit 74 refers to thefirst conversion table table1[4096][3] and decodes E2[n] into datacontained in “table1[D4 [n−3], D4 [n−2], D4 [n−1]][E2[n]−1].”

When E2[n] is “00b,” this is not data loaded in the received firstconversion table table1[4096][3], and thus the decoding unit 74determines the value of E2[n+1].

When E2[n+1] is “01b,” “10b” or “11b,” the decoding unit 74 refers tothe received second conversion table table2[4096][3] and decodes E2[n+1]into data contained in “table2[D4 [n−3], D4 [n−2], D4[n−1]][E2[n+1]−1].”

When E2[n+1] is also “00b,” this is not data loaded in the receivedsecond conversion table table2[4096][3], and thus the decoding unit 74determines the value of E2[n+2].

When E2[n+2] is “01b,” “10b” or “11b,” the decoding unit 74 refers tothe received third conversion table table3[4096][3] and decodes E2[n+1]into data contained in “table3[D4 [n−3], D4 [n−2], D4[n−1]][E2[n+2]−1].”

When E2[n+2] is also “00b,” this is data that is not loaded even in thereceived third conversion table table3[4096][3] and thus 4-bit data“E2[n+3]+E2[n+4]” following E2[n+2] is data to be decoded by thedecoding unit 74.

<Compressive Encoding Method Using 4-stage Conversion Table Table>

Next, a compressive encoding method using first to fourth conversiontables table1 to table4 will be described.

The part of finding a value identical to D4[n] through the firstconversion table table1 to the third conversion table table3 is the sameas that in the aforementioned compressive encoding method using a3-stage conversion table table, and thus description thereof is omitted.

Subsequently, when the three values of the address (column) indicated byD4[n−3], D4[n−2]D4[n−1] of the third conversion table table3[4096][3] donot include data identical to D4[n], the encoding unit 15 searches forthree values, table4[D4 [n−3], D4 [n−2], D4[n−1]][0], table4[D4 [n−3],D4 [n−2], D4[n−1]][1] and table4[D4[n−3], D4[n−2], D4[n−1]][2], of theaddress (column) indicated by D4[n−3], D4[n−2]D4[n−1] of the fourthconversion table table4[4096][3].

When any of the three values, table4[D4[n−3], D4[n−2], D4[n−1]][0],table4[D4[n−3], D4[n−2], D4[n−1]][1], and table4[D4[n−3], D4[n−2],D4[n−1]][2], of the address (column) indicated by D4[n−3], D4[n−2],D4[n−1] of the fourth conversion table table4[4096][3] is identical toD4[n], the encoding unit 15 converts D4[n] into 8 bits of “00000001b” ifD4[n] is identical to table4[D4[n−3], D4[n−2], D4[n−1]][0], convertsD4[n] into 8 bits of “00000010b” if D4[n] is identical totable4[D4[n−3], D4[n−2], D4[n−1]][1] and converts D4[n] into 8 bits of“00000011b” if D4[n] is identical to table4[D4[n−3], D4[n−2],D4[n−1]][2].

On the other hand, when three values of an address (column) indicated byD4[n−3], D4[n−2], D4[n−1] of the fourth conversion table table4[4096][3]do not include a value identical to D4[n], the encoding unit 15 convertsD4[n] to 12 bits by adding “00000000b” before D4[n], such as“00000000b+D4[n].”

<Decoding Method Using 4-stage Conversion Table Table>

Next, a decoding method using the first to fourth conversion tablestable1 to table4 will be described.

In a case in which E2[n] is “00b,” “01b,” “10b” or “11b,” a case inwhich E2[n+1] is “00b,” “01b,” “10b” or “11b” and a case in whichE2[n+2] is “01b,” “10b” or “11b,” the decoding method is the same as theaforementioned decoding method using a 3-stage conversion table tableand thus description thereof is omitted.

When E2[n+2] is also “00b,” this is data that is not loaded even in thereceived third conversion table table3[4096][3], and thus the decodingunit 74 determines the value of E2[n+3].

When E2[n+3] is “01b,” “10b” or “11b,” the decoding unit 74 refers tothe received fourth conversion table table4[4096][3] and decodes E2[n+1]into data contained in “table4[D4[n−3], D4[n−2], D4[n−1]][E2[n+3]−1].”

When E2[n+3] is also “00b,” this is data that is not loaded even in thereceived fourth conversion table table4[4096][3] and thus 4-bit data“E2[n+4]+E2[n+5]” following E2[n+3] is data to be decoded by thedecoding unit 74.

<Compressive Encoding Method Using 5-stage Conversion Table Table>

Next, a compressive encoding method using first to fifth conversiontables table1 to table5 will be described.

The part of finding a value identical to D4[n] through the firstconversion table table1 to the fourth conversion table table4 is thesame as that in the aforementioned compressive encoding method using a4-stage conversion table table, and thus description thereof is omitted.

When the three values of the address (column) indicated by D4[n−3],D4[n−2]D4[n−1] of the fourth conversion table table4[4096][3] do notinclude data identical to D4[n], the encoding unit 15 searches for threevalues, table5[D4 [n−3], D4 [n−2], D4[n−1]][0], table5[D4 [n−3], D4[n−2], D4[n−1]][1] and table5[D4[n−3], D4[n−2], D4[n−1]][2], of theaddress (column) indicated by D4[n−3], D4[n−2]D4[n−1] of the fifthconversion table table5[4096][3].

When any of the three values, table5[D4[n−3], D4[n−2], D4[n−1]][0],table5[D4 [n−3], D4 [n−2], D4[n−1]][1], and table5[D4 [n−3], D4 [n−2],D4[n−1]][2], of the address (column) indicated by D4[n−3], D4[n−2],D4[n−1] of the fifth conversion table table5[4096][3] is identical toD4[n], the encoding unit 15 converts D4[n] into 10 bits of “0000000001b”if D4[n] is identical to table5[D4[n−3], D4[n−2], D4[n−1]][0], convertsD4[n] into 10 bits of “0000000010b” if D4[n] is identical totable5[D4[n−3], D4[n−2], D4[n−1]][1] and converts D4[n] into 10 bits of“0000000011b” if D4 [n] is identical to table5[D4 [n−3], D4 [n−2],D4[n−1]][2].

On the other hand, when three values of an address (column) indicated byD4[n−3], D4[n−2], D4[n−1] of the fifth conversion table table5[4096][3]do not include a value identical to D4[n], the encoding unit 15 convertsD4[n] to 14 bits by adding “0000000000b” before D4[n], such as“0000000000b+D4[n].”

<Decoding Method Using 5-stage Conversion Table Table>

Next, a decoding method using the first to fifth conversion tablestable1 to table5 will be described.

In a case in which E2[n] is “00b,” “01b,” “10b” or “11b,” a case inwhich E2[n+1] is “00b,” “01b,” “10b” or “11b,” a case in which E2[n+2]is “00b,” “01b,” “10b” or “11b,” and a case in which E2[n+3] is “01b,”“10b” or “11b,” the decoding method is the same as the aforementioneddecoding method using a 4-stage conversion table table and thusdescription thereof is omitted.

When E2[n+3] is also “00b,” this is data that is not loaded even in thereceived fourth conversion table table4[4096][3], and thus the decodingunit 74 determines the value of E2[n+3].

When E2[n+4] is “01b,” “10b” or “11b,” the decoding unit 74 refers tothe received fifth conversion table table5[4096][3] and decodes E2[n+1]into data contained in “table5[D4 [n−3], D4 [n−2], D4[n−1]][E2[n+4]−1].”

When E2[n+4] is also “00b,” this is data that is not loaded even in thereceived fifth conversion table table5[4096][3] and thus 4-bit data“E2[n+5]+E2[n+6]” following E2[n+4] is data to be decoded by thedecoding unit 74.

As described above, when DSD data is compressively encoded in units of 4bits on the basis of a conversion table table, compressive encoding isnot limited to a 2-stage conversion table table and may use conversiontables table of 3 or more stages.

Furthermore, although the number of reference bits of past data is 12bits in the aforementioned example, compressive encoding may be equallyperformed even when the number of past reference bits is 16 bits, 20bits or the like as described in the eighth embodiment.

According to the aforementioned ninth embodiment, the compressiveencoding apparatus 1 compressively encodes and transmits DSD data andthe decoding apparatus 70 receives the compressively encoded andtransmitted data, reversibly decodes the received data and outputs thedecoded data. In the ninth embodiment, data of the Q-th conversion tabletable used for compressive encoding are compressed and transmitted astransmission data.

<Example of Processing Result>

FIG. 25 illustrates compression rates when the number of stages ofconversion tables table and the number of reference bits of past dataare changed and a plurality of pieces of content are compressivelyencoded.

Here, a compression rate refers to a value obtained by dividing a dataquantity reduced according to compression by a data quantity beforeencoding (compression rate=data quantity reduced according tocompression/data quantity before encoding).

In the compressive encoding method of the present disclosure, acompression rate becomes a maximum value when DSD data in units of 4bits is necessarily present in a conversion table table and convertedinto 2 bits, and the value (maximum value) is 50% at this time.

Referring to results of compression rates of a plurality of pieces ofcontent illustrated in FIG. 25, compression rates are improved twiceapproximately, for example, 12%→19% (content 1) and 10%→19% (content 2),by increasing the number of stages of conversion tables table from 1 to2, except content 3 having a compression rate of 40% approximate to atheoretical maximum value, when a first-stage conversion table table isused.

Further, according to the results of FIG. 25, compression rates increaseas the number of stages of conversion tables table increases from 1 to2, (3) and 4. When the number of reference bits of past data increasesfrom 12 bits to 20 bits, compression rates also increase slightly.

When compressive encoding is performed using the method of PatentLiterature 1 disclosed as a prior art document and compression rates arecalculated, 0.5% (sample 1), 2.4% (sample 2), 0.4% (sample 3) and thelike are obtained. When the compression and decompression methods of thepresent disclosure are compared with the method of Patent Literature 1disclosed as a prior art document, it is possible to further enhance acorrelation with past data and to further increase compression rates byextending the number of reference bits of past data to 12 bits, 16 bitsor 20 bits. That is, it is possible to provide a lossless compressiontechnology having a higher compression rate.

<10. Tenth Embodiment>

<Example of Configuration of Compressive Encoding Apparatus>

FIG. 26 illustrates an example of a configuration of a tenth embodimentof the compressive encoding apparatus according to the presentdisclosure.

In the tenth embodiment, the controller 14 creates the first to Q-thconversion tables table1 to tableQ on the basis of the previouslycreated data generation count table pretable and supplies the first toQ-th conversion tables table to the encoding unit 15, as in the ninthembodiment illustrated in FIG. 23.

The encoding unit 15 includes a 4-to-2 encoding unit 181 and a 4-to-1encoding unit 182.

The 4-to-2 encoding unit performs compressive encoding of converting DSDdata in units of 4 bits into 2 bits with reference to the Q-stageconversion table as in the ninth embodiment. In this case, while amaximum value of Q is 5, any of 1 to 5 may be employed as the number ofstages.

Whereas, the 4-to-1 encoding unit 182 performs compressive encoding ofconverting DSD data in units of 4 bits into 1 bit with reference to theQ-stage conversion table. In this case, while a maximum value of Q is16, any of 1 to 16 may be employed as the number of stages.

The controller 14 may decide which one of the 4-to-2 encoding unit 181and the 4-to-1 encoding unit 182 will be used for compressive encodingand create the first to Q-th conversion tables table1 to tableQ on thebasis of the previously created data generation count table pretable.

For example, the controller 14 may decide which one of the 4-to-2encoding unit 181 and the 4-to-1 encoding unit 182 will be used forcompressive encoding on the basis of compression rates when initial DSDdata of one frame is compressively encoded using both the 4-to-2encoding unit 181 and the 4-to-1 encoding unit 182 or on the basis ofuser setting through a setting screen and the like or designation from acounterpart apparatus.

Further, the number of stages of conversion tables table may also beappropriately decided in the same manner.

<Example of Configuration of Decoding Apparatus>

FIG. 27 illustrates an example of a configuration of a tenth embodimentof a decoding apparatus according to the present disclosure.

The decoding apparatus 70 of FIG. 27 is an apparatus for receiving anaudio signal compressively encoded and transmitted by the compressiveencoding apparatus 1 of FIG. 26 and decompressing (reversible decoding)the audio signal.

The table storage unit 75 supplies, to the decoding unit 74, the firstconversion table table1 to the Q-th conversion table tableQ that havebeen received by the data receiving unit 72 and decompressed by theconversion table decompression unit 111.

The decoding unit 74 includes a 4-to-2 decoding unit 191 and a 4-to-1decoding unit 192 corresponding to the 4-to-2 encoding unit 181 and a4-to-1 encoding unit 182 of the compressive encoding apparatus 1 of FIG.26.

The decoding unit 74 executes a decoding process using one of the 4-to-2decoding unit 191 and the 4-to-1 decoding unit 192 on the basis of aQ-stage conversion table table supplied from the table storage unit 75.

<Method of Creating Conversion Table>

Next, a method of creating the conversion table table1 by the controller14 when compressive encoding is performed using the 4-to-1 encoding unit182 will be described.

Meanwhile, a method of creating the data generation count table pretableis the same as the method described with reference to FIG. 2 and thusdescription thereof is omitted.

The controller 14 creates the first conversion tabletable1[4096][1]=table1[4096] having 4,096 columns and 1 column on thebasis of the previously created data generation count table pretable.Here, elements [0] to [4095] of the first conversion table table1[4096]correspond to values that may be past three pieces of D4 data, and avalue having a highest generation frequency (first value) from among 16values of the following D4 data is contained in the values of the pastthree pieces of D4 data.

FIG. 28 illustrates an example of the first conversion tabletable1[4096] when compressive encoding is performed using the 4-to-1encoding unit 182.

As described with reference to FIG. 2, a value having a highestgeneration frequency (first value) is “5” which has been generated 31times in pretable[117][0] to [117][15] which is the 118^(th) column ofthe data generation count table pretable, and thus {05} is contained inthe 118^(th) element of the first conversion table table1[4096].

FIG. 29 illustrates an example of the second conversion tabletable2[4096] when compressive encoding is performed using the 4-to-1encoding unit 182.

As described with reference to FIG. 2, a value having a second highestgeneration frequency is “4” which has been generated 20 times inpretable[117][0] to [117][15] which is the 118^(th) column of the datageneration count table pretable, and thus {04} is contained in the118^(th) element of the second conversion table table2[4096].

In the same manner, up to the sixteenth conversion table table16[4096]may be created by sequentially selecting values from a value having ahigher generation frequency.

<Compressive Encoding Method Using 4-to-1 Encoding Unit 182>

Next, a compressive encoding method using the 4-to-1 encoding unit 182and a decoding method using the 4-to-1 decoding unit 192 will bedescribed.

<Compressive Encoding Using Only First Conversion Table Table1>

First, a compressive encoding method using only the first conversiontable table1 will be described.

In a way similar to the above description, a case in which the encodingunit 15 encodes D4[n] from among DSD data . . . D4[n−3], D4[n−2],D4[n−1], D4[n], D4[n+1], D4[n+2], D4[n+3], . . . supplied from the inputbuffer 13 will be described.

When D4[n] is encoded, the encoding unit 15 regards D4[n−3], D4[n−2],D4[n−1], which is past 12-bit data immediately before D4[n], as a massof 12-bit data and determines whether a value contained in addressvalues indicated by D4[n−3], D4[n−2], D4[n−1] of the first conversiontable table1[4096], that is, table1[D4[n−3], D4[n−2], D4[n−1]] isidentical to D4[n].

When it is determined that a value contained in table1[D4[n−3], D4[n−2],D4[n−1]] is identical to D4[n], the encoding unit 15 converts D4[n] into1 bit of “1b.”

On the other hand, when it is determined that no value contained intable1[D4[n−3], D4[n−2], D4[n−1]] is identical to D4[n], the encodingunit 15 converts D4[b] into 5 bits by adding “0b” before D4[n] such as“0b+D4[n].” Here, b in “0b+D4[n]” represents binary notation.

<Decoding Using Only First Conversion Table Table1>

Next, a decoding method using only the first conversion table table1will be described.

A description will be given of a case in which compressed data which hasbeen compressively encoded by the 4-to-1 encoding unit 182 andtransmitted therefrom is represented in units of 1 bit as follows andE1[n] is decoded.

-   . . . E1[n−3], E1[n−2], E1[n−1], E1[n], E1[n+1], E1[n+2], E1[n+3], .    . . .

The decoding unit 74 first determines the value of E1[n].

When E1[n] is “0b,” this is not data loaded in the received firstconversion table table1[4096], and thus 4-bit data “E1[n+1]+E1[n+2]+E1[n+3]+E1[n+4]” following E1[n] is data to be decoded.

On the other hand, when E1[n] is “1b,” this is data loaded in the firstconversion table table1[4096], and thus data to be decoded is searchedwith reference to the first conversion table table1[4096] using 12-bitD4 data D4[n−3], D4[n−2], D4[n−1] which has been decoded immediatelybefore E1[n].

<Compressive Encoding Using First Conversion Table Table1 and SecondConversion Table Table2>

Next, a compressive encoding method using the first conversion tabletable1 and the second conversion table table2 will be described.

When D4[n] is encoded, the encoding unit 15 regards D4[n−3], D4[n−2],D4[n−1], which is past 12-bit data immediately before D4[n], as a massof 12-bit data and determines whether a value contained in addressvalues indicated by D4[n−3], D4[n−2], D4[n−1] of the first conversiontable table1[4096], that is, table1[D4 [n−3], D4 [n−2], D4[n−1]] isidentical to D4 [n].

When it is determined that a value contained in table1[D4[n−3], D4[n−2],D4[n−1]] is identical to D4[n], the encoding unit 15 converts D4[n] into1 bit of “1b.”

On the other hand, when it is determined that no value contained intable1[D4[n−3], D4[n−2], D4[n−1]] is identical to D4[n], the encodingunit 15 determines whether a value contained in address values indicatedby D4[n−3], D4[n−2], D4[n−1] of the second conversion tabletable2[4096], that is, table2[D4[n−3], D4[n−2], D4[n−1]], is identicalto D4[n].

When it is determined that a value contained in table2[D4[n−3], D4[n−2],D4[n−1]] is identical to D4[n], the encoding unit 15 converts D4[n] into2 bits of “01b.”

On the other hand, when it is determined that no value contained intable2[D4[n−3], D4[n−2], D4[n−1]] is identical to D4[n], the encodingunit 15 converts D4[b] into 6 bits by adding “0b” before D4[n] such as“00b+D4[n].” Here, b in “00b+D4[n]” represents binary notation.

<Decoding Using First Conversion Table Table1 and Second ConversionTable Table2>

Next, a decoding method using the first conversion table table1 and thesecond conversion table table2 will be described.

First of all, the decoding unit 74 determines the value of E1[n].

When E1 [n] is “0b,” this is not data loaded in the received firstconversion table table1[4096][3], and thus the decoding unit 74determines the value of E1[n+1].

When E1[n+1] is also “0b,” this is not data loaded in the receivedsecond conversion table table2[4096][3], and thus 4-bit data“E1[n+2]+E1[n+3]+E1[n+4]+E1[n+5]” following E1[n+1] is data to bedecoded.

On the other hand, when E1[n] is “1b,” this is data loaded in thereceived first conversion table table1[4096] and thus data to be decodedis searched for with reference to the first conversion tabletable1[4096] using 12-bit D4 data D4[n−3], D4[n−2], D4[n−1] which hasbeen decoded immediately before E2[n]. The data to be decoded is datacontained in “table1[D4[n−3], D4[n−2], D4[n−1]].”

On the other hand, when E1[n+1] is “1b,” this is data loaded in thereceived second conversion table table2[4096] and thus data to bedecoded is searched for with reference to the second conversion tabletable2[4096] using 12-bit D4 data D4[n−3], D4[n−2], D4[n−1] which hasbeen decoded immediately before E2[n]. The data to be decoded is datacontained in “table2[D4[n−3], D4[n−2], D4[n−1]].”

This similarly applies to a compressive encoding method and a decodingmethod using the first to third conversion tables table1 to table3 to acompressive encoding method and a decoding method using the first tofifteenth conversion tables table1 to table15, and thus descriptionthereof is omitted.

<Compressive Encoding Using 16-stage Conversion Table Table>

Finally, a compressive encoding method using the first to sixteenthconversion tables table1 to table16 will be described.

The part of searching the first to fifteenth conversion tables table1 totable15 for a value identical to D4[n] is the same as the abovedescription and thus description thereof is omitted.

When it is determined that no value contained in table15[D4[n−3],D4[n−2], D4[n−1]] is identical to D4[n], D4[n] is identical to a valuecontained in address values indicated by D4[n−3], D4[n−2], D4[n−1] ofthe sixteenth conversion table table16[4096], that is, table16[D4[n−3],D4[n−2], D4[n−1]], and thus the encoding unit 15 converts D4[n] into 16bits of “0000000000000001b.”

<Decoding Using 16-stage Conversion Table>

Next, a decoding method using the first to sixteenth conversion tablestable1 to table16 will be described.

The part of determining whether E1[n] to E1[n+15] in the first tofifteenth conversion tables table1 to table 15 are “0b” or “1b” is thesame as the above description and thus description thereof is omitted.

When all of E1[n] to E1[n+15] are “0b,” E1[n] to E1[n+15] are data thatare not loaded in any of the received first to fifteenth conversiontables table1[4096] to table15[4096] and thus they are data loaded inthe sixteenth conversion table table16[4096]. Accordingly, data to bedecoded is searched with reference to the sixteenth conversion tabletable16[4096] using 12-bit D4 data D4[n−3], D4[n−2], D4[n−1] decodedimmediately before E1[n] to E1[n+15]. The data to be decoded is datacontained in “table16[D4[n−3], D4[n−2], D4[n−1]].”

According to the aforementioned tenth embodiment, the compressiveencoding apparatus 1 compressively encodes and transmits DSD data andthe decoding apparatus 70 receives the transmission data compressivelyencoded and transmitted, reversibly decodes the received data andoutputs the decoded data. In the tenth embodiment, it is possible toselect compressive encoding of converting 4-bit DSD data into 2 bits orcompressive encoding of converting the 4-bit DSD data into 1 bit. Dataof the Q-stage conversion table table used for compressive encoding iscompressed and transmitted as transmission data.

<11. 11th Embodiment>

<Example of Configuration of Compressive Encoding Apparatus>

FIG. 30 illustrates an example of a configuration of an 11th embodimentof the compressive encoding apparatus according to the presentdisclosure.

In the eleventh embodiment illustrated in FIG. 30, the encoding unit 15includes the 4-to-2 encoding unit 181 and the 4-to-1 encoding unit 182as in the tenth embodiment illustrated in FIG. 26.

The controller 14 previously stores a 4-to-2 conversion table table usedfor encoding performed by the 4-to-2 encoding unit 181 and a 4-to-1conversion table table used for encoding performed by the 4-to-1encoding unit 182.

That is, while the compressive encoding apparatus 1 in the eleventhembodiment has a configuration in which any of compressive encoding ofconverting 4-bit DSD data into 2 bits and compressive encoding ofconverting the 4-bit DSD data into 1 bit may be selected with referenceto the Q-stage conversion table as in the tenth embodiment, the Q-stageconversion table table is not created using the transmitted DSD data butis previously stored as in the sixth embodiment illustrated in FIG. 17.

The controller 14 decides which one of the 4-to-2 encoding unit 181 andthe 4-to-1 encoding unit 182 will be used for compressive encoding andsupplies the 4-to-2 conversion table table or the 4-to-1 conversiontable table corresponding to the decision result to the encoding unit15.

In addition, the controller 14 supplies conversion table designationdata which indicates the selected conversion table table to the datatransmission unit 18.

Meanwhile, only one type of conversion table is stored as the 4-to-2conversion table table and the 4-to-1 conversion table table in theexample of FIG. 30, a plurality of types of conversion tables may bestored for the 4-to-2 conversion table table and the 4-to-1 conversiontable table as in the eighth embodiment described with reference to FIG.21.

<Example of Configuration of Decoding Apparatus>

FIG. 31 illustrates an example of a configuration of an 11th embodimentof a decoding apparatus according to the present disclosure.

The decoding apparatus 70 of FIG. 31 is an apparatus for receiving anaudio signal compressively encoded and transmitted by the compressiveencoding apparatus 1 of FIG. 30 and decompressing (reversible decoding)the audio signal.

The decoding unit 74 includes the 4-to-2 decoding unit 191 and the4-to-1 decoding unit 192 corresponding to the 4-to-2 encoding unit 181and the 4-to-1 encoding unit 182 of the compressive encoding apparatus 1of FIG. 30.

The table storage unit 75 previously stores a 4-to-2 conversion tabletable and a 4-to-1 conversion table table identical to those included inthe controller 14 of the compressive encoding apparatus 0 of FIG. 30.

The data receiving unit 72 supplies conversion table designation dataincluded in received data to the table storage unit 75. The tablestorage unit 75 supplies one of the 4-to-2 conversion table table andthe 4-to-1 conversion table table, which is indicated by the conversiontable designation data supplied from the data receiving unit 72, to thedecoding unit 74.

The decoding unit 74 executes a decoding process using the 4-to-2decoding unit 191 or the 4-to-1 decoding unit 192 on the basis of the4-to-2 conversion table table or the 4-to-1 conversion table tablesupplied from the table storage unit 75.

According to the aforementioned eleventh embodiment, the compressiveencoding apparatus 1 compressively encodes and transmits DSD data andthe decoding apparatus 70 receives the transmission data compressivelyencoded and transmitted, reversibly decodes the received data andoutputs the decoded data. In the eleventh embodiment, it is possible toselect compressive encoding of converting 4-bit DSD data into 2 bits orcompressive encoding of converting the 4-bit DSD data into 1 bit. Dataof the Q-stage conversion table table used for compressive encoding ispreviously stored.

<Example of Processing Results>

FIG. 32 illustrates an example of processing results according to the4-to-2 encoding unit 181 and the 4-to-1 encoding unit 182.

All the processing results of FIG. 32 are common when the number ofreference bits of past data is 20 bits and the number of stages ofconversion tables is 4.

Referring to the compressive encoding results illustrated in FIG. 32, itcan be known that, for content which has compression rates approximateto a theoretical maximum value (50%) when 4 bits are compressivelyencoded into 2 bits, compression rates can be further increased bycompressively encoding 4 bits into 1 bit through the 4-to-1 encodingunit 182.

In the above-described embodiments, the example of performingcompressive encoding by converting 4 bits into 2-bit code using a dataconversion table table based on data generation frequency for a digitalsignal (DSD data) ΔΣ-modulated by the ADC 12 has been described.Further, the example of performing compressive encoding by converting 4bits into 1-bit code has also been described.

However, the compressive encoding apparatus 1 may compressively encode 8bits by converting the 8 bits into a 4-bit code, for example, and thedecoding apparatus 70 may decompress (reversibly decode) the codecompressively encoded by the compressive encoding apparatus 1. When 8bits are converted into 4-bit code, the register 51 of the encoding unit15 in FIG. 4 is modified to store 8 bits and the register 54 is modifiedto store 4 bits, for example. In addition, the register 91 of thedecoding unit 74 in FIG. 6 is modified to store 4 bits and the register94 is modified to store 8 bits.

Accordingly, the compressive encoding apparatus 1 may include theencoding unit 15 which converts M bits of a ΔΣ-modulated digital signalinto N bits (M>N) with reference to the first conversion table table1and, when the M bits cannot be converted into the N bits using the firstconversion table table1, converts the M bits into the N bits withreference to the second conversion table table2. Here, when the numberof bit patterns of the N bits is P, the first conversion table table1 isa table storing (P−1) number of codes having higher generationfrequencies for past bit patterns, and the second conversion tabletable2 is a table storing (P−1) number of codes having higher generationfrequencies for past bit patterns, which follow those of the firstconversion table table1.

Furthermore, the decoding apparatus 70 may include the decoding unit 74which converts N bits of encoded data, which has been obtained bycompressively encoding M bits of a ΔΣ-modulated digital signal into theN bit (M>N), into the M bits with reference to the first conversiontable table1 and, when the N bits cannot be converted into the M bitsusing the first conversion table table1, decodes the N bits into the Mbits with reference to the second conversion table table2. Here, whenthe number of bit patterns of the N bits is P, the first conversiontable table1 is a table storing (P−1) number of codes having highergeneration frequencies for past bit patterns, and the second conversiontable table2 is a table storing (P−1) number of codes having highergeneration frequencies for past bit patterns, which follow those of thefirst conversion table table1.

In the compressive encoding apparatus 1 and the decoding apparatus 70,the functions of embodiments described in the first to tenth embodimentsare not limited to the described combinations and an arbitrarycombination of part or all of the functions of the embodiments may beemployed. In addition, the arbitrary combined functions may beappropriately selected and executed depending on various conditions suchas user setting, traffic or capacity of a network (communication line),processing capability (CPU power and memory capacity) of an apparatus,and designation from an apparatus at a receiving side.

For example, compressive encoding using a multi-stage conversion tablewith 2 or more stages having a higher compression rate may be performedwhen network traffic is large or line capacity is small, whereascompressive encoding using only a one-stage conversion table may beselected when a network is light.

Further, compressive encoding using a previously stored conversion tabletable without transmitting conversion table data may be performed whennetwork traffic is large or line capacity is small, whereas data of aconversion table table created from actual DSD data may be transmittedas it is or compressed and transmitted such that a decoding side usesthe data when a network is light, for example.

Further, compressive encoding may be selected such that compressiveencoding using only a one-stage conversion table is performed whenprocessing capability of a decoding apparatus of a receiving side islow, whereas compressive encoding using a multi-stage conversion tabletable having 2 or more stages may used when the processing capability ofthe decoding apparatus of the receiving side is high, for example.

In addition, the compressive encoding apparatus 1 may transmit data of aconversion table table created from actual DSD data as it is or aftercompressing the same when performing compressive encoding using only aone-stage conversion table and uses a previously stored conversion tabletable when performing compressive encoding using a multi-stageconversion table table having 2 or more stages, for example.

<Example of Application to Computer>

The above-described series of processes may be executed by hardware orsoftware. The compression and decompression methods of the presentdisclosure do not depend on device processing capability becausethroughput according to software processing of a central processing unit(CPU) is low. Accordingly, the compression and decompression methodshave low device type dependence for mobile terminals, stationary devicesand the like.

When the series of processes described above is executed by software, aprogram that constructs such software is installed into a computer.Here, the expression “computer” includes a computer in which dedicatedhardware is incorporated and a general-purpose personal computer or thelike that is capable of executing various functions when variousprograms are installed.

FIG. 33 is a block diagram showing an example configuration of thehardware of a computer that executes the series of processes describedearlier according to a program.

In the computer, a CPU 201, a read only memory (ROM) 202 and a randomaccess memory (RAM) 203 are mutually connected by a bus 204.

An input/output interface 205 is also connected to the bus 204. An inputunit 206, an output unit 207, a storage unit 208, a communication unit209, and a drive 210 are connected to the input/output interface 205.

The input unit 206 is configured from a keyboard, a mouse, a microphoneor the like. The output unit 207 configured from a display, a speaker orthe like. The storage unit 208 is configured from a hard disk, anon-volatile memory or the like. The communication unit 209 isconfigured from a network interface or the like. The drive 210 drives aremovable recording medium 211 such as a magnetic disk, an optical disk,a magneto-optical disk, a semiconductor memory or the like.

In the computer configured as described above, the CPU 201 loads aprogram that is stored, for example, in the storage unit 208 onto theRAM 203 via the input/output interface 205 and the bus 204, and executesthe program. Thus, the above-described series of processing isperformed.

In the computer, by loading the removable recording medium 211 into thedrive 210, the program can be installed into the storage unit 208 viathe input/output interface 205. It is also possible to receive theprogram from a wired or wireless transfer medium such as a local areanetwork, the Internet, digital satellite broadcasting, etc., using thecommunication unit 209 and install the program into the storage unit208. As another alternative, the program can be installed in advanceinto the ROM 202 or the storage unit 208.

It should be noted that the program executed by a computer may be aprogram that is processed in time series according to the sequencedescribed in this specification or a program that is processed inparallel or at necessary timing such as upon calling.

An embodiment of the disclosure is not limited to the embodimentsdescribed above, and various changes and modifications may be madewithout departing from the scope of the disclosure.

For example, it is possible to employ a combination of all or part ofthe above-described multiple embodiments.

For example, the present disclosure can adopt a configuration of cloudcomputing which processes by allocating and connecting one function by aplurality of apparatuses through a network.

Further, each step described by the above-mentioned flow charts can beexecuted by one apparatus or by allocating a plurality of apparatuses.

In addition, in the case where a plurality of processes are included inone step, the plurality of processes included in this one step can beexecuted by one apparatus or by sharing a plurality of apparatuses.

Note that the effects described in the present specification are notlimiting but are merely examples, and there may be additional effects.

Additionally, the present technology may also be configured as below.

-   (1)

A compressive encoding apparatus including

an encoding unit that converts M bits of a ΔΣ-modulated digital signalinto N bits (M>N) with reference to a first conversion table, and whenthe M bits are not able to be converted into the N bits with the firstconversion table, converts the M bits into the N bits with reference toa second conversion table,

in which, when the number of bit patterns of the N bits is P,

-   -   the first conversion table is a table storing (P−1) number of        codes having higher generation frequencies for past bit        patterns, and    -   the second conversion table is a table storing (P−1) number of        codes having higher generation frequencies for past bit        patterns, which follow those of the first conversion table.

-   (2)

The compressive encoding apparatus according to (2), further including

a data transmission unit that transmits converted data converted by theencoding unit,

in which the data transmission unit transmits data of the firstconversion table and the second conversion table along with theconverted data.

(3)

The compressive encoding apparatus according to (2), further including

a conversion table compression unit that creates compressed conversiontable data in which the data of the first conversion table and thesecond conversion table is compressed,

in which the data transmission unit transmits the compressed conversiontable data as the data of the first conversion table and the secondconversion table.

-   (4)

The compressive encoding apparatus according to any of (1) to (3), inwhich the first conversion table and the second conversion table aretables created using the digital signal.

(5)

The compressive encoding apparatus according to any of (1) to (4),including

a storage unit that stores a plurality of sets of the first conversiontable and the second conversion table,

in which the encoding unit converts the M bits into the N bits using aset of the first conversion table and the second conversion tableselected from the plurality of sets.

-   (6)

The compressive encoding apparatus according to (5), in which a sethaving a highest compression rate is selected from the plurality of setsof the first conversion table and the second conversion table stored inthe storage unit.

-   (7)

The compressive encoding apparatus according to any of (1) to (6),

in which the number of bits of the past bit patterns are provided as aplurality of types, and

the encoding unit converts the M bits into the N bits using a set of thefirst conversion table and the second conversion table having apredetermined number of bits selected from the plurality of types.

-   (8)

The compressive encoding apparatus according to any of (1) to (7),

in which the encoding unit converts the M bits into the N bits withreference to a third conversion table when the M bits are not able to beconverted into the N bits with the second conversion table, and

the third conversion table is a table storing (P−1) number of codeshaving higher generation frequencies for past bit patterns, which followthose of the second conversion table.

-   (9)

The compressive encoding apparatus according to any of (1) to (8), inwhich the encoding unit includes a first encoding unit that converts theM bits of the digital signal into the N bits and a second encoding unitthat converts the M bits of the digital signal into N2 bits differentfrom the N bits.

-   (10)

The compressive encoding apparatus according to (9), further including

a storage unit that stores a set of the first conversion table and thesecond conversion table for the first encoding unit and a set of thefirst conversion table and the second conversion table for the secondencoding unit.

-   (11)

A compressive encoding method including

converting M bits of a ΔΣ-modulated digital signal into N bits (M>N)with reference to a first conversion table, and when the M bits are notable to be converted into the N bits with the first conversion table,converting the M bits into the N bits with reference to a secondconversion table,

in which, when the number of bit patterns of the N bits is P,

-   -   the first conversion table is a table storing (P−1) number of        codes having higher generation frequencies for past bit        patterns, and    -   the second conversion table is a table storing (P−1) number of        codes having higher generation frequencies for past bit        patterns, which follow those of the first conversion table.

-   (12)

A program that causes a computer to execute a process of converting Mbits of a ΔΣ-modulated digital signal into N bits (M>N) with referenceto a first conversion table, and when the M bits are not able to beconverted into the N bits with the first conversion table, convertingthe M bits into the N bits with reference to a second conversion table,

in which, when the number of bit patterns of the N bits is P,

-   -   the first conversion table is a table storing (P−1) number of        codes having higher generation frequencies for past bit        patterns, and    -   the second conversion table is a table storing (P−1) number of        codes having higher generation frequencies for past bit        patterns, which follow those of the first conversion table.        (13)

A decoding apparatus including

a decoding unit that converts N bits of encoded data that is obtained bycompressively encoding M bits (M>N) of a ΔΣ-modulated digital signalinto the N bits, into the M bits with reference to a first conversiontable, and when the N bits are not able to be converted into the M bitswith the first conversion table, decodes the N bits into the M bits withreference to a second conversion table,

in which, when the number of bit patterns of the N bits is P,

-   -   the first conversion table is a table storing (P−1) number of        codes having higher generation frequencies for past bit        patterns, and    -   the second conversion table is a table storing (P−1) number of        codes having higher generation frequencies for past bit        patterns, which follow those of the first conversion table.

-   (14)

The decoding apparatus according to (13), further including

a data receiving unit that receives the encoded data,

in which the data receiving unit receives data of the first conversiontable and the second conversion table along with the encoded data.

-   (15)

The decoding apparatus according to (13), including

a storage unit that stores a plurality of sets of the first conversiontable and the second conversion table,

in which the decoding unit converts the N bits into the M bits using aset of the first conversion table and the second conversion tableselected from the plurality of sets.

-   (16)

The decoding apparatus according to (15), further including

a data receiving unit that receives conversion table designation datadesignating the set of the first conversion table and the secondconversion table that is selected from the plurality of sets, along withthe encoded data.

-   (17)

The decoding apparatus according to any of (13) to (16),

in which the decoding unit converts the N bits into the M bits withreference to a third conversion table when the M bits are not able to beconverted with the second conversion table, and

the third conversion table is a table storing (P−1) number of codeshaving higher generation frequencies for past bit patterns, which followthose of the second conversion table.

-   (18)

The decoding apparatus according to any of (13) to (16), in which thedecoding unit includes a first decoding unit that converts the N bits ofthe encoded data into the M bits and a second decoding unit thatconverts N2 bits of the encoded data different from the N bits, into theM bits.

-   (19)

A decoding method including

converting N bits of encoded data that is obtained by compressivelyencoding M bits (M>N) of a ΔΣ-modulated digital signal into the N bits,into the M bits with reference to a first conversion table, and when theN bits are not able to be converted into the M bits with the firstconversion table, decoding the N bits into the M bits with reference toa second conversion table,

in which, when the number of bit patterns of the N bits is P,

-   -   the first conversion table is a table storing (P−1) number of        codes having higher generation frequencies for past bit        patterns, and    -   the second conversion table is a table storing (P−1) number of        codes having higher generation frequencies for past bit        patterns, which follow those of the first conversion table.

-   (20)

A program that causes a computer to execute a process of converting Nbits of encoded data that is obtained by compressively encoding M bits(M>N) of a ΔΣ-modulated digital signal into the N bits, into the M bitswith reference to a first conversion table, and when the N bits are notable to be converted into the M bits with the first conversion table,decoding the N bits into the M bits with reference to a secondconversion table,

in which, when the number of bit patterns of the N bits is P,

-   -   the first conversion table is a table storing (P−1) number of        codes having higher generation frequencies for past bit        patterns, and    -   the second conversion table is a table storing (P−1) number of        codes having higher generation frequencies for past bit        patterns, which follow those of the first conversion table.

REFERENCE SIGNS LIST

-   1 compressive encoding apparatus-   14 controller-   15 encoding unit-   18 data transmission unit-   53 conversion table processing unit-   70 decoding apparatus-   72 data receiving unit-   74 decoding unit-   75 table storage unit-   93 conversion table processing unit-   111 conversion table decompression unit-   141 12-bit reference encoding unit-   142 16-bit reference encoding unit-   143 20-bit reference encoding unit-   161 12-bit reference decoding unit-   162 16-bit reference decoding unit-   163 20-bit reference decoding unit-   181 4-to-2 encoding unit-   182 4-to-1 encoding unit-   191 4-to-2 decoding unit-   192 4-to-1 decoding unit-   201 CPU-   202 ROM-   203 RAM-   206 input unit-   207 output unit-   208 storage unit-   209 communication unit-   210 drive

The invention claimed is:
 1. A compressive encoding apparatuscomprising: an encoding unit that converts M bits of a ΔΣ-modulateddigital signal into N bits (M>N) with reference to a first conversiontable, and when the M bits are not able to be converted into the N bitswith the first conversion table, converts the M bits into the N bitswith reference to a second conversion table, wherein, when the number ofbit patterns of the N bits is P, the first conversion table is a tablestoring (P−1) number of codes having higher generation frequencies forpast bit patterns, and the second conversion table is a table storing(P−1) number of codes having higher generation frequencies for past bitpatterns, which follow those of the first conversion table; and a datatransmission unit that transmits converted data converted by theencoding unit, wherein the data transmission unit transmits data of thefirst conversion table and the second conversion table along with theconverted data.
 2. The compressive encoding apparatus according to claim1, further comprising: a conversion table compression unit that createscompressed conversion table data in which the data of the firstconversion table and the second conversion table is compressed, whereinthe data transmission unit transmits the compressed conversion tabledata as the data of the first conversion table and the second conversiontable.
 3. The compressive encoding apparatus according to claim 1,wherein the first conversion table and the second conversion table aretables created using the digital signal.
 4. The compressive encodingapparatus according to claim 1, comprising: a storage unit that stores aplurality of sets of the first conversion table and the secondconversion table, wherein the encoding unit converts the M bits into theN bits using a set of the first conversion table and the secondconversion table selected from the plurality of sets.
 5. The compressiveencoding apparatus according to claim 4, wherein a set having a highestcompression rate is selected from the plurality of sets of the firstconversion table and the second conversion table stored in the storageunit.
 6. The compressive encoding apparatus according to claim 1,wherein the number of bits of the past bit patterns are provided as aplurality of types, and the encoding unit converts the M bits into the Nbits using a set of the first conversion table and the second conversiontable having a predetermined number of bits selected from the pluralityof types.
 7. The compressive encoding apparatus according to claim 1,wherein the encoding unit converts the M bits into the N bits withreference to a third conversion table when the M bits are not able to beconverted into the N bits with the second conversion table, and thethird conversion table is a table storing (P−1) number of codes havinghigher generation frequencies for past bit patterns, which follow thoseof the second conversion table.
 8. The compressive encoding apparatusaccording to claim 1, wherein the encoding unit includes a firstencoding unit that converts the M bits of the digital signal into the Nbits and a second encoding unit that converts the M bits of the digitalsignal into N2 bits different from the N bits.
 9. The compressiveencoding apparatus according to claim 8, further comprising: a storageunit that stores a set of the first conversion table and the secondconversion table for the first encoding unit and a set of the firstconversion table and the second conversion table for the second encodingunit.
 10. A compressive encoding method comprising: converting M bits ofa ΔΣ-modulated digital signal into N bits (M>N) with reference to afirst conversion table, and when the M bits are not able to be convertedinto the N bits with the first conversion table, converting the M bitsinto the N bits with reference to a second conversion table, wherein,when the number of bit patterns of the N bits is P, the first conversiontable is a table storing (P−1) number of codes having higher generationfrequencies for past bit patterns, and the second conversion table is atable storing (P−1) number of codes having higher generation frequenciesfor past bit patterns, which follow those of the first conversion table;and transmitting converted data and transmitting data of the firstconversion table and the second conversion table along with theconverted data.
 11. A non-transitory computer-readable medium storinginstructions that, when executed by a processing device, cause theprocessing device to perform a process of converting M bits of aΔΣ-modulated digital signal into N bits (M>N) with reference to a firstconversion table, and when the M bits are not able to be converted intothe N bits with the first conversion table, converting the M bits intothe N bits with reference to a second conversion table, wherein, whenthe number of bit patterns of the N bits is P, the first conversiontable is a table storing (P−1) number of codes having higher generationfrequencies for past bit patterns, and the second conversion table is atable storing (P−1) number of codes having higher generation frequenciesfor past bit patterns, which follow those of the first conversion table.12. A decoding apparatus comprising: a decoding unit that converts Nbits of encoded data that is obtained by compressively encoding M bits(M>N) of a ΔΣ-modulated digital signal into the N bits, into the M bitswith reference to a first conversion table, and when the N bits are notable to be converted into the M bits with the first conversion table,decodes the N bits into the M bits with reference to a second conversiontable, wherein, when the number of bit patterns of the N bits is P, thefirst conversion table is a table storing (P−1) number of codes havinghigher generation frequencies for past bit patterns, and the secondconversion table is a table storing (P−1) number of codes having highergeneration frequencies for past bit patterns, which follow those of thefirst conversion table.
 13. The decoding apparatus according to claim12, further comprising: a data receiving unit that receives the encodeddata, wherein the data receiving unit receives data of the firstconversion table and the second conversion table along with the encodeddata.
 14. The decoding apparatus according to claim 12, comprising: astorage unit that stores a plurality of sets of the first conversiontable and the second conversion table, wherein the decoding unitconverts the N bits into the M bits using a set of the first conversiontable and the second conversion table selected from the plurality ofsets.
 15. The decoding apparatus according to claim 14, furthercomprising: a data receiving unit that receives conversion tabledesignation data designating the set of the first conversion table andthe second conversion table that is selected from the plurality of sets,along with the encoded data.
 16. The decoding apparatus according toclaim 12, wherein the decoding unit converts the N bits into the M bitswith reference to a third conversion table when the M bits are not ableto be converted with the second conversion table, and the thirdconversion table is a table storing (P−1) number of codes having highergeneration frequencies for past bit patterns, which follow those of thesecond conversion table.
 17. The decoding apparatus according to claim12, wherein the decoding unit includes a first decoding unit thatconverts the N bits of the encoded data into the M bits and a seconddecoding unit that converts N2 bits of the encoded data different fromthe N bits, into the M bits.
 18. A decoding method comprising:converting N bits of encoded data that is obtained by compressivelyencoding M bits (M>N) of a ΔΣ-modulated digital signal into the N bits,into the M bits with reference to a first conversion table, and when theN bits are not able to be converted into the M bits with the firstconversion table, decoding the N bits into the M bits with reference toa second conversion table, wherein, when the number of bit patterns ofthe N bits is P, the first conversion table is a table storing (P−1)number of codes having higher generation frequencies for past bitpatterns, and the second conversion table is a table storing (P−1)number of codes having higher generation frequencies for past bitpatterns, which follow those of the first conversion table.
 19. Anon-transitory computer-readable medium storing instructions that, whenexecuted by a processing device, cause the processing device to performa process of converting N bits of encoded data that is obtained bycompressively encoding M bits (M>N) of a ΔΣ-modulated digital signalinto the N bits, into the M bits with reference to a first conversiontable, and when the N bits are not able to be converted into the M bitswith the first conversion table, decoding the N bits into the M bitswith reference to a second conversion table, wherein, when the number ofbit patterns of the N bits is P, the first conversion table is a tablestoring (P−1) number of codes having higher generation frequencies forpast bit patterns, and the second conversion table is a table storing(P−1) number of codes having higher generation frequencies for past bitpatterns, which follow those of the first conversion table.